FAQ 47 (the Memories FAQ) has information about deleting memories, but it doesn't mention what happens when you try to delete a memory that leads to a deleted entry. At least judging from support requests, there are people that try the standard "edit memory to erase the description" method, get an error, and get confused.
I'd like to suggest that something like the following be added as a separate paragraph at the end of the DELETING MEMORIES section:
If the memory points to a deleted entry, or to an entry in a deleted journal, you will need to use the multidelete method to delete the memory. Memories of deleted entries cannot be edited.