The drawback of this change is that it would cause orb to fail with older versions of GAP. So one would have to update GAP and orb at the same time, and failing to do so (updating only one but not the other) would either result in an error, or wrong results / a crash.

In this case, it should be quite easy to make the orb code more robust, though: Just keep the old HashKeyBak code, and use something like this:
```
if IsBound(HASH_FUNC_FOR_TRANS) then
  InstallGlobalFunction( ORB_HashFunctionForTransformations, HASH_FUNC_FOR_TRANS);
elif CompareVersionNumbers(GAPInfo.Version,"4.7") then
  ... old code follows ...
```