Reproducible: Always
What was I doing right before the crash: I was spectating, then my game freezed. I forced it to alt+tab instead of restart the computer and I crashed.
What you think caused the crash: Alt+Tabbing on class selection/spectate screen
Crash Report:

Exception At Address: 0x1000B861

Registers:
EAX: 0x43160000 EBX: 0x00000000 ECX: 0x00000000 EDX: 0x43DE38E4
ESI: 0x1006DB6E EDI: 0x0012FB8E EBP: 0xFFFFFFFF ESP: 0x0012F938
EFLAGS: 0x00010202

Stack:
0x02683C90
0x77D2808B
0x5B1ED0B8
0x00000015
0x0012F9A8
0x5B1C2D56
0x77D244DE
0x77D258E9
0x001601A4
0x00000020
0x001601A4
0x77D244DE
0x77D258E9
0x001601A4
0x0000000F
0x00000000
0x00000000
0x00000000
0x0000029E
0x00000001
0x0012FB1C
0x0000000F
0x00460C12
0x00000000
0x0000000B