added shouldRetainData check - checks BlockRotation to see if they have the same rotation type, implying their blockData has the same meaning.

blockrotation.py

@@ -361,12 +361,24 @@ def masterRotationTable(attrname):
 
     return table
 
+def rotationTypeTable():
+    table = {}
+    for cls in rotationClasses:
+        for b in cls.blocktypes:
+            table[b] = cls
+    
+    return table
+    
 class BlockRotation:
     rotateLeft = masterRotationTable("rotateLeft");
     flipEastWest = masterRotationTable("flipEastWest");
     flipNorthSouth = masterRotationTable("flipNorthSouth");
     flipVertical = masterRotationTable("flipVertical");
+    typeTable = rotationTypeTable()
     
+def SameRotationType(blocktype1, blocktype2):
+    #use different default values for typeTable.get() to make it return false when neither blocktype is present
+    return BlockRotation.typeTable.get(blocktype1.ID) == BlockRotation.typeTable.get(blocktype2.ID, BlockRotation)
     
 def FlipVertical(blocks, data):
     data[:] = BlockRotation.flipVertical[blocks, data]

infiniteworld.py

@@ -2419,6 +2419,7 @@ class MCInfdevOldLevel(EntityLevel):
 
         if len(blocksToReplace):
             blocktable = self.blockReplaceTable(blocksToReplace)
+            shouldRetainData = all([blockrotation.SameRotationType(blockInfo, b) for b in blocksToReplace])
         
             newAbsorption = self.materials.lightAbsorption[blockInfo.ID]
             oldAbsorptions = [self.materials.lightAbsorption[b.ID] for b in blocksToReplace]

level.py

@@ -344,8 +344,9 @@ class MCLevel(object):
         blocks = self.Blocks[slices[0], slices[2], slices[1]]
         if len(blocksToReplace):
             blocktable = self.blockReplaceTable(blocksToReplace)
+            shouldRetainData = (self.materials == alphaMaterials) and all([blockrotation.SameRotationType(blockInfo, b) for b in blocksToReplace])
             
-            if hasattr(self, "Data"):
+            if hasattr(self, "Data") and shouldRetainData:
                 data = self.Data[slices[0], slices[2], slices[1]]
                 mask = blocktable[blocks, data]