Steps to reproduce, Via window phones or windows 8 plex clients (I also think it might have happend with a Android client, but not 100% sure) start some music controlling the rasplex client, while music is playing change the music, do this a few times and the raspberry Pi restarts (Get the openelec/rasplex gui logo)
Server is version 0.9.9.0 also happend on the 0.9.8.x version running on a Drobo5N
Seems to happen reasonably consistently, but not every single time
I think you may have to accept that the RPi is a low-end computer, and remotely starting a new playback thread while another is already running may sometimes be too much for it to handle, though it would work fine when done on a more powerful computer.
I'm not sure exactly what controls you have in the remote apps since I have an RF-connected miniature USB keyboard as remote for my RPi. On that I simply press the X key to terminate playback before choosing some new media to play.
True the Pi is low powered, but at this point as I am just playing music the system is not under load (approx. 33% CPU and with free memory), this smells to me like a race condition, especially as it happens inconsistently.
If I get some time I will setup a Dev environment and have a look and brush off my cpp skills (It has been a long time!).
