When I first looked at this issue, it appeared to me reading the code that the assumption was not considered safe.  I'm hoping I can implement something akin to your algorithm in email6 (which, unfortunately, won't make 3.2), but I'm going to have to give it a lot of thought to make sure I'm not making any unsafe assumptions.  So while I have this issue on my list, it won't be addressed in 3.2.