Just saying me too (also to get informed about news on this front). It happenes both on reboot and shutdown attempts.
I can also offer to help debugging it, if there's something specific I can do (in jessie). Also, I'd suggest to increase the severity, since, you know, not shutting down the system properly seems a pretty big deal to me. For all its perceived weaknesses, sysvinit has been able to do that for decades. (I'm getting used to shut down by raising elephants -- still easier to do than manually doing swapoff every time -- but that really can't be the way to go.):
