Open the "Auxiliary keys" dialog multiple times, check that the key is no longer incremented each time.
Open the Proof editor, check that the key is the same as the one currently shown by default in the keys dialog. Close and reopen the Proof editor, nothing changes.
Generate a proof with the suggested key, check that now the index has been incremented.
Open the delegation editor, generate a delegated key using the suggested one. Check again that this does not affect the index. Generate a delegation with the suggested key, check that the index is now incremented.
Load a proof whose master key is not from this wallet, check that generating the (unsigned) proof does not increment the index.
Generate a proof with a WIF key that does not belong to this wallet, check that the index is not incremented.