I have to admit I've had some freaky things happening with PMs too. None of them make any sense, and they aren't reproducible at will.
1. Sometimes, for absolutely no reason that I can figure out, some people just don't get a PM that's been sent to them. I've only seen this happen about four times - one of those times it was me who sent the PM. When looking at the Participants, only I'm on the list. Weird ...
This happens to me too. I think what it is ... is that they have deleted their original PM, and once they delete it, you can no longer respond to it. You have to start a new one. I have found this with our site, and I find it highly annoying.
