Microsoft are aware and have admitted its an OS bug, OTA update coming in December:
Microsoft plans OTA update to keep Windows Phone 8 devices from randomly rebooting
Had another 2 reboots in the past 24hrs not related to SmartGlass at all. Must just be a buggy HTC implementation of WP8 that we will have to wait for them to patch.
I have the same problem with a new HTC 8x, and after reading this thread and the apps scumpuppy removed in the 2nd batch removed Xbox Smartglass which was the only common app.
So far no reboots in the past 24hrs but not getting over excited yet...