Registered Users Editing Own Comments

Running the current 1.5 branch it seems that the ability for users to edit their own comments after posting isn’t fully supported. In fact, I can’t seem to figure out any reason behind which posts a user can edit and which they cannot. Is there some secret? My users are all set at level 5, but which posts they can edit seems practically random. Searching the forums indicates that this is a known problem of some kind (read: unsupported).

And has this been improved in 2.0?