diff --git a/spec/System/TestPowerReport_spec.lua b/spec/System/TestPowerReport_spec.lua
index a98126e5751..899c5e57ad0 100644
--- a/spec/System/TestPowerReport_spec.lua
+++ b/spec/System/TestPowerReport_spec.lua
@@ -36,3 +36,136 @@ describe("PowerReportListControl", function()
 		assert.are.equal("allocated", list[1].name)
 	end)
 end)
+
+describe("Power report cluster calculations", function()
+	local calcsTab, originalCalculator, originalTime, originalProgress, originalComplete
+	local clusterNodes, clusterCalls, hitDPS
+
+	before_each(function()
+		newBuild()
+		runCallback("OnFrame")
+		calcsTab = build.calcsTab
+		calcsTab.nodePowerMaxDepth = 1
+		originalCalculator = calcsTab.miscCalculator[1]
+		originalTime = GetTime
+		originalProgress = build.powerBuilderProgressCallback
+		originalComplete = build.powerBuilderCallback
+		clusterNodes = { }
+		clusterCalls = 0
+		for _, node in pairs(build.spec.tree.clusterNodeMap) do
+			clusterNodes[node] = true
+		end
+		for _, stat in ipairs(data.powerStatList) do
+			if stat.stat == "TotalDPS" then
+				hitDPS = stat
+				break
+			end
+		end
+		calcsTab.miscCalculator[1] = function(mod, ...)
+			for node in pairs(mod.addNodes or { }) do
+				if clusterNodes[node] then
+					clusterCalls = clusterCalls + 1
+					break
+				end
+			end
+			return originalCalculator(mod, ...)
+		end
+	end)
+
+	after_each(function()
+		calcsTab.miscCalculator[1] = originalCalculator
+		_G.GetTime = originalTime
+		build.powerBuilderProgressCallback = originalProgress
+		build.powerBuilderCallback = originalComplete
+		calcsTab.powerBuilder = nil
+		calcsTab.powerBuildFlag = false
+		build.treeTab.viewer.showHeatMap = false
+	end)
+
+	it("skips cluster calculations for Offence/Defence while initializing power tables", function()
+		calcsTab.powerStat = data.powerStatList[1]
+		calcsTab:PowerBuilder()
+		assert.are.equal(0, clusterCalls)
+		assert.is_not_nil(next(clusterNodes))
+		for node in pairs(clusterNodes) do
+			assert.same({ }, node.power)
+		end
+	end)
+
+	it("clears Hit DPS cluster values in Offence/Defence and restores them on returning", function()
+		calcsTab.powerStat = hitDPS
+		calcsTab:PowerBuilder()
+		assert.is_true(clusterCalls > 0)
+		local initialCalls = clusterCalls
+		local initialPowers = { }
+		for node in pairs(clusterNodes) do
+			initialPowers[node] = copyTable(node.power)
+			if not node.alloc and node.modKey ~= "" and not calcsTab.mainEnv.grantedPassives[node.id] then
+				assert.is_number(node.power.singleStat)
+			end
+		end
+
+		clusterCalls = 0
+		calcsTab.powerStat = data.powerStatList[1]
+		calcsTab:PowerBuilder()
+		assert.are.equal(0, clusterCalls)
+		for node in pairs(clusterNodes) do
+			assert.same({ }, node.power)
+		end
+
+		calcsTab.powerStat = hitDPS
+		calcsTab:PowerBuilder()
+		assert.are.equal(initialCalls, clusterCalls)
+		for node in pairs(clusterNodes) do
+			assert.same(initialPowers[node], node.power)
+		end
+	end)
+
+	it("reports progress and completes only the replacement after a metric switch", function()
+		local clock = 0
+		_G.GetTime = function()
+			clock = clock + 101
+			return clock
+		end
+		-- Exercise real traversal and coroutine scheduling without repeating the stat calculations.
+		calcsTab.miscCalculator[1] = function()
+			return calcsTab.miscCalculator[2]
+		end
+		local progress = { }
+		local completions = 0
+		build.powerBuilderProgressCallback = function(percent)
+			assert.is_true(percent >= 0 and percent <= 100)
+			assert.is_true(percent >= (progress[#progress] or 0))
+			table.insert(progress, percent)
+		end
+		build.powerBuilderCallback = function()
+			completions = completions + 1
+			originalComplete()
+		end
+
+		build.treeTab:SetPowerCalc(hitDPS)
+		calcsTab:BuildPower()
+		local abandonedBuilder = calcsTab.powerBuilder
+		calcsTab:BuildPower()
+		assert.is_true(#progress > 0)
+		assert.are.equal(0, completions)
+		build.treeTab:SetPowerCalc(data.powerStatList[1])
+		assert.same({ }, build.treeTab.controls.powerReportList.originalList)
+		progress = { }
+		calcsTab:BuildPower()
+		assert.is_not.equal(abandonedBuilder, calcsTab.powerBuilder)
+		for _ = 1, 10000 do
+			if not calcsTab.powerBuilder then
+				break
+			end
+			calcsTab:BuildPower()
+		end
+		assert.is_nil(calcsTab.powerBuilder)
+		assert.is_true(#progress > 0)
+		assert.are.equal(1, completions)
+		assert.same({ }, build.treeTab.controls.powerReportList.originalList)
+		assert.are.equal("suspended", coroutine.status(abandonedBuilder))
+		calcsTab:BuildPower()
+		assert.are.equal(1, completions)
+	end)
+end)
diff --git a/src/Classes/CalcsTab.lua b/src/Classes/CalcsTab.lua
index 7d79e865d98..76db1855b4d 100644
--- a/src/Classes/CalcsTab.lua
+++ b/src/Classes/CalcsTab.lua
@@ -496,6 +496,7 @@ end
 function CalcsTabClass:PowerBuilder()
 	-- local timer_start = GetTime()
 	local useFullDPS = self.powerStat and self.powerStat.stat == "FullDPS"
+	local useClusterPower = self.powerStat and self.powerStat.stat and not self.powerStat.ignoreForNodes
 	local calcFunc, calcBase = self:GetMiscCalculator()
 	local cache = { }
 	local distanceMap = { }
@@ -597,9 +598,11 @@ function CalcsTabClass:PowerBuilder()
 	distanceMap = nil
 	table.sort(distanceList, function(a, b) return a[1] < b[1] end)
 	-- Count eligible cluster nodes
-	for _, node in pairs(self.build.spec.tree.clusterNodeMap) do
-		if not node.alloc and node.modKey ~= "" and not self.mainEnv.grantedPassives[node.id] then
-			total = total + 1
+	if useClusterPower then
+		for _, node in pairs(self.build.spec.tree.clusterNodeMap) do
+			if not node.alloc and node.modKey ~= "" and not self.mainEnv.grantedPassives[node.id] then
+				total = total + 1
+			end
 		end
 	end
 
@@ -716,14 +719,12 @@ function CalcsTabClass:PowerBuilder()
 			node.power = {}
 		end
 		wipeTable(node.power)
-		if not node.alloc and node.modKey ~= "" and not self.mainEnv.grantedPassives[node.id] then
+		if useClusterPower and not node.alloc and node.modKey ~= "" and not self.mainEnv.grantedPassives[node.id] then
 			if not cache[node.modKey] then
 				cache[node.modKey] = calcFunc({ addNodes = { [node] = true } }, useFullDPS)
 			end
 			local output = cache[node.modKey]
-			if self.powerStat and self.powerStat.stat and not self.powerStat.ignoreForNodes then
-				node.power.singleStat = self:CalculatePowerStat(self.powerStat, output, calcBase)
-			end
+			node.power.singleStat = self:CalculatePowerStat(self.powerStat, output, calcBase)
 			nodeIndex = nodeIndex + 1
 			if coroutine.running() and GetTime() - start > 100 then
 				if self.build.powerBuilderProgressCallback then