diff --git a/examples/regression_jbeam/y-sorting-repro.jbeam b/examples/regression_jbeam/y-sorting-repro.jbeam
index 2e3f2f13..87e9ec38 100644
--- a/examples/regression_jbeam/y-sorting-repro.jbeam
+++ b/examples/regression_jbeam/y-sorting-repro.jbeam
@@ -2,10 +2,16 @@
 "testpart":{
     "nodes":[
         ["id", "posX", "posY", "posZ"],
-        // Synthetic regression-test fixture for issue #214, not vetted by
-        // the jbeam maintainer and not intended as a demo/example.
+        // Synthetic regression-test fixture, not vetted by the jbeam
+        // maintainer and not intended as a demo/example.
         // Real node positions from a gen4-style body file, reduced to just
-        // the left side, kept because this spacing reproduces a real bug.
+        // the left side, kept because this spacing reproduces two real bugs.
+        // Issue #214: at y-sorting-threshold 0.1 the frontmost node sorts to
+        // the back of its group.
+        // X columns: the five frontmost nodes sit in two vertical columns
+        // that Y and Z cannot separate, so a band sorted by Z alone climbs
+        // one column, jumps to the other and comes back.
+        // Change these positions and both tests are measuring something else.
         ["nl0", 0.953, -1.967, 0.122],
         ["nl2", 0.92, -1.953, 0.439],
         ["nl4", 0.78, -1.815, 0.719],
diff --git a/src-extra/transformation/JbeamEdit/Transformation/Config.hs b/src-extra/transformation/JbeamEdit/Transformation/Config.hs
index 6579da3e..f58141eb 100644
--- a/src-extra/transformation/JbeamEdit/Transformation/Config.hs
+++ b/src-extra/transformation/JbeamEdit/Transformation/Config.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE MultiWayIf #-}
 
 module JbeamEdit.Transformation.Config (
   loadTransformationConfig,
@@ -18,6 +19,7 @@ import Control.Monad (forM, when)
 import Data.Bifunctor (first)
 import Data.ByteString.Lazy qualified as LBS
 import Data.Functor (($>))
+import Data.Maybe (isJust, isNothing)
 import Data.Scientific (Scientific)
 import Data.Text (Text)
 import Data.Text qualified as T
@@ -46,6 +48,9 @@ import Numeric.Natural (Natural)
 import System.OsPath
 import Text.Read
 
+defaultXSortingThreshold :: Maybe Scientific
+defaultXSortingThreshold = Nothing
+
 defaultSortingThreshold :: Scientific
 defaultSortingThreshold = 0.05
 
@@ -65,6 +70,7 @@ defaultBreakpoints =
 
 data TransformationConfig = TransformationConfig
   { ySortingThreshold :: Scientific
+  , xSortingThreshold :: Maybe Scientific
   , xGroupBreakpoints :: XGroupBreakpoints
   , supportThreshold :: Scientific
   , maxSupportCoordinates :: Natural
@@ -75,6 +81,7 @@ newTransformationConfig :: TransformationConfig
 newTransformationConfig =
   TransformationConfig
     defaultSortingThreshold
+    defaultXSortingThreshold
     defaultBreakpoints
     defaultSupportThreshold
     defaultMaxSupportCoordinates
@@ -134,10 +141,25 @@ parseSupportThreshold o = do
       fail
         "'support-threshold' must be a percentage value of 1 or higher (e.g., 80 or 80.8). Values below 1 (e.g., 0.80) are not allowed."
 
+parseXSortingThreshold :: Object -> Parser (Maybe Scientific)
+parseXSortingThreshold o = do
+  thr <- o .:? "x-sorting-threshold"
+  let cleanThr = T.unpack . T.strip <$> thr
+      maybeValid = cleanThr >>= readMaybe
+   in if
+        | thr == Just "off" || isNothing thr -> pure defaultXSortingThreshold
+        | isJust maybeValid -> pure maybeValid
+        | True -> failWithMessage
+  where
+    failWithMessage =
+      fail
+        "TODO: proper error message"
+
 instance FromJSON TransformationConfig where
   parseJSON = withObject "TransformationConfig" $ \o ->
     TransformationConfig
       <$> o .:? "y-sorting-threshold" .!= defaultSortingThreshold
+      <*> parseXSortingThreshold o
       <*> o .:? "x-group-breakpoints" .!= defaultBreakpoints
       <*> parseSupportThreshold o
       <*> o .:? "max-support-coordinates" .!= defaultMaxSupportCoordinates
diff --git a/test-extra/transformation/Spec.hs b/test-extra/transformation/Spec.hs
index ce7067c5..23b89f18 100644
--- a/test-extra/transformation/Spec.hs
+++ b/test-extra/transformation/Spec.hs
@@ -157,6 +157,7 @@ main = hspec $ do
   supportRenameIdempotencySpec
   letterEndingNodesSpec
   ySortingBandingSpec
+  xColumnSortingSpec
   metadataAcrossTreesSpec
   metadataPreservedSpec
   triangleMetadataSpec
diff --git a/test-extra/transformation/Spec/Helpers.hs b/test-extra/transformation/Spec/Helpers.hs
index 07ae87d4..2b8b944f 100644
--- a/test-extra/transformation/Spec/Helpers.hs
+++ b/test-extra/transformation/Spec/Helpers.hs
@@ -2,6 +2,7 @@
 module Spec.Helpers (
   parseJbeamFile,
   vertexPositionsInOrder,
+  vertexCoordinatesInOrder,
   vertexCoordinates,
   effectiveMetaByCoordinate,
   metaNumber,
@@ -53,6 +54,25 @@ vertexPositionsInOrder topNode =
       , Just (Number yNum) <- [inner V.!? 2]
       ]
 
+{- | Every vertex coordinate in a top node's "nodes" section, in the order
+`transform` wrote them out. Use this where the defect is about which vertex
+ended up where, rather than about which vertices survived.
+-}
+vertexCoordinatesInOrder :: Node -> [(Double, Double, Double)]
+vertexCoordinatesInOrder topNode =
+  case NP.queryNodes nodesQuery topNode >>= NP.expectArray nodesQuery of
+    Left _ -> []
+    Right rows ->
+      [ (realToFrac (nvValue x), realToFrac (nvValue y), realToFrac (nvValue z))
+      | row <- V.toList rows
+      , Just inner <- [expectArray row]
+      , Just (String name) <- [inner V.!? 0]
+      , name /= "id"
+      , Just (Number x) <- [inner V.!? 1]
+      , Just (Number y) <- [inner V.!? 2]
+      , Just (Number z) <- [inner V.!? 3]
+      ]
+
 {- | Every vertex coordinate in a top node's "nodes" section. Positions
 survive renaming, so they identify a vertex across a transform.
 -}
diff --git a/test-extra/transformation/Spec/Regression.hs b/test-extra/transformation/Spec/Regression.hs
index ff041164..69425272 100644
--- a/test-extra/transformation/Spec/Regression.hs
+++ b/test-extra/transformation/Spec/Regression.hs
@@ -9,6 +9,7 @@ module Spec.Regression (
   ySortingBandingSpec,
   metadataAcrossTreesSpec,
   metadataPreservedSpec,
+  xColumnSortingSpec,
 ) where
 
 import Data.Map qualified as M
@@ -171,3 +172,43 @@ metadataPreservedSpec =
                 ]
           M.keys metaAfter `shouldBe` M.keys metaBefore
           changed `shouldBe` []
+
+{- | The same gen4-style left-side positions as the y-sorting fixture, read
+for a different defect. Its five frontmost nodes sit in two vertical
+columns: an inner one at X 0.780/0.920/0.953 and an outer one at X
+0.998/1.036, the nose face and the fender beside it. Y and Z interleave
+between the two columns, so no y-sorting-threshold can separate them; only
+X can. Sorting a band by Z alone therefore climbs one column, jumps to the
+other and comes back, which is what the jbeam maintainer marked up on his
+render.
+
+The Y threshold here is 0.31 rather than the default because that is what puts
+all five in one band, which is where the defect lives. It is not free choice:
+between 0.153 and 0.16 the Y bands land on exactly the two columns, and this
+assertion passes with nothing fixed at all.
+
+`xSortingThreshold` has to be set explicitly because it has no default. There is
+no number that means off (0 gives every vertex its own band, which is the most
+X sorting rather than none), so the field is optional and absent means the pass
+does not run at all.
+-}
+xColumnSortingSpec :: Spec
+xColumnSortingSpec =
+  describe "vertices in one Y band but different X columns"
+    . it "keeps each column contiguous instead of interleaving them"
+    $ do
+      let cfg =
+            newTransformationConfig
+              { ySortingThreshold = 0.31
+              , xSortingThreshold = Just 0.2
+              }
+          inner = [(0.953, -1.967, 0.122), (0.92, -1.953, 0.439), (0.78, -1.815, 0.719)]
+          outer = [(1.036, -1.807, 0.125), (0.998, -1.791, 0.473)]
+      topNode <- parseJbeamFile ySortingReproFixture
+      case transform M.empty cfg topNode of
+        Left err -> expectationFailure ("transform failed: " ++ T.unpack err)
+        Right (_, _, _, resultNode) ->
+          take 5 (leftGroup (vertexCoordinatesInOrder resultNode))
+            `shouldBe` inner ++ outer
+  where
+    leftGroup = filter (\(x, _, _) -> x >= 0.09)