Suppose a transaction opens a cursor, then abandons it. The locks for that cursor will be held in intent mode, even between batches.

Now suppose a drop for the database or collection comes in. That drop will "get in line" with a MODE_X lock. In order to be fair to such requests, that pending MODE_X acquisition will block all future intent acquisitions. 

This will prevent a killCursors from killing the cursor, since it will need to take a collection lock. It looks like it will also prevent the background transaction timeout job from killing it.