Index: /trunk/src/VBox/Devices/Storage/VDIHDDCore.cpp
===================================================================
--- /trunk/src/VBox/Devices/Storage/VDIHDDCore.cpp	(revision 33029)
+++ /trunk/src/VBox/Devices/Storage/VDIHDDCore.cpp	(revision 33030)
@@ -2138,5 +2138,6 @@
             }
 
-            if (cbToWrite == getImageBlockSize(&pImage->Header))
+            if (   cbToWrite == getImageBlockSize(&pImage->Header)
+                && !(fWrite & VD_WRITE_NO_ALLOC))
             {
                 /* Full block write to previously unallocated block.