Daniel The Medic
Somewhat Threatening Sniper
The last 3 times this happened, (3 updates) it was related to multicore processing issues for me.
I just needed to go into to my settings and disabled them even though they they were already disabled.
Every time i restarted TF2 i had to do this as the settings stopped being saved or being handled properly.
If you want to do research on when this bug first popped up, its like November 2011. (maybe even earlier, its been around a long time)
When TF2 first went F2P I remember having issues with multicore rendering causing weird stuff and crashes.
Not anymore though. I run mat_queue_mode 2 in autoexec.cfg and have TF2 set with threaded optimization to ON in nvidia settings (I recently switched from ATI to nVidia).