I'm not sure why I was successful the first time I tried it, but I haven't been able to replicate that success. However, it wasn't dsme triggering the reboot, but one of the watchdogs, I put my N900 into R&D mode and disabled the watchdogs and now it just locks up for a while rather than rebooting, and I did at least get some interesting debug output in dmesg, I guess it is some sort of issue with the USB drivers that pulseaudio presumably triggers, I've attached the relevant dmesg output to this post and maybe someone will be able to make sense of it.