diff --git a/blockrotation.py b/blockrotation.py
index fa4688b..d67e81a 100644
--- a/blockrotation.py
+++ b/blockrotation.py
@@ -361,13 +361,25 @@ 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]
 
diff --git a/infiniteworld.py b/infiniteworld.py
index 03fdc70..1a46961 100644
--- a/infiniteworld.py
+++ b/infiniteworld.py
@@ -2412,14 +2412,15 @@ class MCInfdevOldLevel(EntityLevel):
         #if shouldRetainData:
         #    info( "Preserving data bytes" )
         shouldRetainData = False #xxx old behavior overwrote blockdata with 0 when e.g. replacing water with lava
-
+       
         info("Replacing {0} with {1}".format(blocksToReplace, blockInfo))
 
         changesLighting = True
 
         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]
             changesLighting = False
diff --git a/level.py b/level.py
index 7bf943a..a83c6f8 100644
--- a/level.py
+++ b/level.py
@@ -340,12 +340,13 @@ class MCLevel(object):
         info(u"Filling blocks in {0} with {1}, replacing{2}".format(box, blockInfo, blocksToReplace))
 
         slices = map(slice, box.origin, box.maximum)
-
+        
         blocks = self.Blocks[slices[0], slices[2], slices[1]]
         if len(blocksToReplace):
             blocktable = self.blockReplaceTable(blocksToReplace)
-
-            if hasattr(self, "Data"):
+            shouldRetainData = (self.materials == alphaMaterials) and all([blockrotation.SameRotationType(blockInfo, b) for b in blocksToReplace])
+            
+            if hasattr(self, "Data") and shouldRetainData:
                 data = self.Data[slices[0], slices[2], slices[1]]
                 mask = blocktable[blocks, data]