This is a typical copy-paste error:
if some Delphi code containing interface declarations with GUIDs is copy-pasted, Delphi will not complain and compile code which re-uses the same GUID in different places.
The "Supports" function works with interfaces based on their GUID, so errors are possible.
Is there a 'quality assurance' tool available (Peganza or the Delphi Sonar plugin maybe) which can detect them?