tested with Deck 0.3.0 and NC 13.0.0 RC1
Steps to reproduce
- Assign a user ("D") to a card
- Delete the user in NC
- Open the board again

Expected behaviour
The deleted user is deassigned from all cards
Actual behaviour
- The deleted user is not deassigned from the card
- The avatar in the card has the "correct" color of the deleted user
- In the right property-view there is a assigned user with "?", which I can't remove in the pop-up