compression.md

@@ -70,8 +70,11 @@ Please note that the source and destinations might overlap
 [memmove](https://en.cppreference.com/w/c/string/byte/memmove#Notes)).
 
 Please note that the offset value could be 0. This would result in
-undefined behavior during decompression, and such a stream should
-be considered invalid.
+undefined behavior during decompression (if the implementation does
+not use exactly the same in-place buffer decompression logic).
+Such streams should be considered invalid. The same problem arises
+from offsets that point before the begin of the decompression buffer
+(also not verified in the original decompression routine).
 
 
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