Via CentralAuth you suppress a global account (some local accounts of the global one are locally blocked *without* hideuser). Later you notice that using suppression was a mistake so you uncheck the global suppression option.
The result is that, if the account was locally blocked, it remains suppressed so you need to manually unsuppress it's name and edits on every project.
Happened today at:
Please note that the "hidden" flag only removes it from Special:GlobalUsers but nothing more.