"on faction changed" causes a bug in editor

The "on faction changed" trigger in the editor has a field for the entity it's supposed to listen to, and is labeled "leave blank for all".  However, if you don't specify a specific map unit, it says there's a bug and won't compile the map.  This makes this trigger nearly useless, as you will almost always want to trigger on many units changing faction; not just pre-placed ones.