diff --git a/examples/regression_jbeam/mirrored-columns-repro.jbeam b/examples/regression_jbeam/mirrored-columns-repro.jbeam
new file mode 100644
index 00000000..2f7ea004
--- /dev/null
+++ b/examples/regression_jbeam/mirrored-columns-repro.jbeam
@@ -0,0 +1,28 @@
+{
+"testpart":{
+    "nodes":[
+        ["id", "posX", "posY", "posZ"],
+        // Synthetic regression-test fixture, not vetted by the jbeam
+        // maintainer and not intended as a demo/example.
+        //
+        // Two columns per side, mirrored across the centre line, at one
+        // station so only the columns can decide the order. X is compared
+        // raw, so the left side runs from the centre outwards while the
+        // right side runs from the outside in, and no existing fixture has
+        // both sides in columns to show it.
+        ["nl0", 0.40, -1.00, 0.10],
+        ["nl1", 0.40, -1.00, 0.50],
+        ["nl2", 0.80, -1.00, 0.10],
+        ["nl3", 0.80, -1.00, 0.50],
+        ["nr0", -0.40, -1.00, 0.10],
+        ["nr1", -0.40, -1.00, 0.50],
+        ["nr2", -0.80, -1.00, 0.10],
+        ["nr3", -0.80, -1.00, 0.50],
+    ],
+    "beams":[
+        ["id1:", "id2:"],
+        ["nl0", "nl1"],
+        ["nr0", "nr1"],
+    ],
+},
+}
diff --git a/test-extra/transformation/Spec.hs b/test-extra/transformation/Spec.hs
index eda6c24b..a2240838 100644
--- a/test-extra/transformation/Spec.hs
+++ b/test-extra/transformation/Spec.hs
@@ -162,6 +162,7 @@ main = hspec $ do
   letterEndingNodesSpec
   ySortingBandingSpec
   xColumnSortingSpec
+  mirroredColumnsSpec
   metadataAcrossTreesSpec
   metadataPreservedSpec
   triangleMetadataSpec
diff --git a/test-extra/transformation/Spec/Config.hs b/test-extra/transformation/Spec/Config.hs
index 5394401f..e7e5d520 100644
--- a/test-extra/transformation/Spec/Config.hs
+++ b/test-extra/transformation/Spec/Config.hs
@@ -14,6 +14,7 @@ import Data.Text (Text)
 import Data.Text qualified as T
 import Data.Text.Encoding (encodeUtf8)
 import JbeamEdit.Transformation.Config
+import JbeamEdit.Transformation.Types (Axis (..), SortAxes (..))
 import Test.Hspec
 
 parseField :: (TransformationConfig -> a) -> Text -> Either Text a
@@ -76,6 +77,27 @@ configParsingSpec = describe "the transformation config parser" $ do
   it "rejects a support-threshold below 1" $
     parseField supportThreshold "support-threshold: 0.8\n" `shouldSatisfy` isLeft
 
+  it "reads a permutation of the three axes" $ do
+    pendingWith
+      "sort-axes has no key in the parser yet, so a config naming one is \
+      \accepted and then ignored, and the file sorts by the default axes \
+      \without saying so. Issue #243."
+    parseField sortAxes (olderThresholds <> "sort-axes: [X, Y, Z]\n")
+      `shouldBe` Right (SortAxes AxisX AxisY AxisZ)
+
+  it "rejects a list that is not three distinct axes" $ do
+    pendingWith
+      "the same missing key, from the other side: a repeated or short list \
+      \has to be refused where it is written, not silently replaced by the \
+      \default. Issue #243."
+    parseField sortAxes (olderThresholds <> "sort-axes: [X, X, Y]\n")
+      `shouldSatisfy` isLeft
+    parseField sortAxes (olderThresholds <> "sort-axes: [X, Y]\n")
+      `shouldSatisfy` isLeft
+
+  it "gives the axes the tool has always used when the key is absent" $
+    parseField sortAxes olderThresholds `shouldBe` Right defaultSortAxes
+
   it "gives every default for an empty file" $ do
     parseField ySortingThreshold "" `shouldBe` Right defaultSortingThreshold
     parseField supportThreshold "" `shouldBe` Right defaultSupportThreshold
diff --git a/test-extra/transformation/Spec/Regression.hs b/test-extra/transformation/Spec/Regression.hs
index 71aaf418..373e0630 100644
--- a/test-extra/transformation/Spec/Regression.hs
+++ b/test-extra/transformation/Spec/Regression.hs
@@ -10,6 +10,7 @@ module Spec.Regression (
   metadataAcrossTreesSpec,
   metadataPreservedSpec,
   xColumnSortingSpec,
+  mirroredColumnsSpec,
 ) where
 
 import Data.Map qualified as M
@@ -220,3 +221,31 @@ xColumnSortingSpec =
       case transform M.empty columnSortingConfig node of
         Left err -> expectationFailure ("transform failed: " ++ T.unpack err)
         Right (_, _, _, resultNode) -> assert resultNode
+
+{- | Both sides of a car hold the same shape mirrored, so the order the
+transform writes them in should mirror too. `compareAV` and the column pass
+compare X as written, and the sides have opposite signs, so the left side is
+walked from the centre outwards and the right side from the outside in.
+
+Which direction both should take is still open, so the assertion says only
+that they agree.
+-}
+mirroredColumnsFixture :: FilePath
+mirroredColumnsFixture =
+  "examples/regression_jbeam/mirrored-columns-repro.jbeam"
+
+mirroredColumnsSpec :: Spec
+mirroredColumnsSpec =
+  describe "two sides holding mirrored columns"
+    . it "writes them back in mirrored order"
+    $ do
+      topNode <- parseJbeamFile mirroredColumnsFixture
+      case transform M.empty newTransformationConfig topNode of
+        Left err -> expectationFailure ("transform failed: " ++ T.unpack err)
+        Right (_, _, _, resultNode) -> do
+          let coordinates = vertexCoordinatesInOrder resultNode
+              left = filter (\(x, _, _) -> x > 0) coordinates
+              right = filter (\(x, _, _) -> x < 0) coordinates
+              mirror (x, y, z) = (negate x, y, z)
+          left `shouldNotBe` []
+          map mirror right `shouldBe` left