If two clients (not necessarily concurrently) try to insert a new "basic" reference without a name, both will be given a listKey value of auto/0. This causes a collision and eventually a crash.

This happens because the value of ve.dm.InternalList#nextUniqueNumber is private to each client and is not part of the document state, so the other clients don't know that it's been incremented. Of course this would also cause problems with concurrency, but it fails even without that.