A local rename on a wiki interferes with a checkuser. When an offencing account has been locked and hidden globally, it should be listed when performing a checkuser. However, when the offencing account name has been renamed locally prior to performing a usercheck, the CU-interface lists the old username. Mediawiki does not display "(locked)" anymore though, which hinders appropriate reaction and tracking of offencing account name vandals.
Probably, the reason might be that mediawiki compares the usernames where user ID/SUL ID number should be compared (or the reverse).