can't remove letter enqueued in user's dashboard

[yourcelf]

When you are in the edit docs page or the user back end you have the correspondence queue on the right.

1. Add a letter (or invitation etc.) or whatever.
2. Try to delete it, and it will not disappear.
3. Clearing the cache and refreshing the page does not remove it either.
4. Add another letter and then that will replace the other letter.
5. Mark the letter as "sent" and you will get Server error /correspondence/letters.json/32934