Yes, it's broken somehow. Deleting users isn't trivial, since every user is referenced in a bunch of game stats and forum posts. My usual solution is to hide the account and to lock it. This will make sure that it won't show up anywhere. If people are worried about their email address still being stored on the server you can change that as well. Just replace it with something random.
@blaataap: Maybe a more recent MojoPortal version would fix this?
Cheers,
Simon