No, not reproducible, so maybe a random crash then, but it was the first reboot I have had since I started using MIUI 3 weeks ago (and on stock I had reboots several times a week) and it came while playing music, and then i read this thread.
I had this happening today on my SGS2 with 2.10.12 while playing music with 3.part music player. The music started to stutter for a few seconds, and then it soft-booted. I didn't have any pattern or pin activated.