I think this is a bug, as it worked earlier (maybe related to 1.19 but I've no real proof).
When an account is blocked locally on every wikis it exists, it should not be able to create automatically a new account on other wikis.
There's no real benefit if a guy who is blocked on every projects he has an account on creates one other account. If the guy has been blocked indefinitely, that's for a valuable reason. Somebody which is block on every projects he has an account on is far more likely to move to an other project to vandalize if the bug is not fixed.
Thanks by advance.