Edi,
I've attached the files I touched along with a little test application.
I basically added a function to the ffi.lisp file call same-objects that takes two C# references from lisp and returns true if they are the same underlying C# object.
I added the respective code to DotNetReference and DotNetContainer as suggested.
I don't know if what I did fits with the overall architecture. Please modify it to match any guidelines that you have.
Let me know if there are any problems.
Regards,
Matthew