Editing Lists of Model Type doesn't work right in old-style Editor

Summary: In Read Access is much too leaky, the top Task was accidentally deleted right after I created it, but seems to have taken anyway. Now, it's just stuck there: I can't delete it, move it, or anything.

Doing some experiments, I can repro this easily, but it's apparently limited to the old Editor -- these operations work fine in the new Thing Editor. That reduces the priority somewhat.