As opposite to what legacy admin did, in Platform Ui it's possible to send users to the trash.
Once you do it you may want to empty the trash completely and this will try to delete all contents in the trash.

But when one of this contents in trash is a user, user entry still remains in ezuser table and this became a huge problem.
first, loadUserByLogin and loadUsersByEmail method in UserService will still get those entries from the ezuser table, but as ezcontentobject related record has indeed be delated, a content not found exception will be thrown

Second, you can't use that login for a new possible user anymore, even if theorically was deleted.

So, as spoken with Bertrand, we have some possible solutions|actions need to be made

• fix in PlatformUI (the button should call delete, not trash, when in user section)
• Alternative would be to override the TrashController as well.
• create a cleanup script for people that may have used this option in the past
• tweak content/trash api so they refuse to delete users until we have a better solution for this

Here's a screencast. sorry for the noise, didn't know microphone was on
https://www.youtube.com/watch?v=VHcbYcQhTrA