The same thing is happening to me. I'll be able to connect to my Host PC through my remote PCs browser but twice my Host PC has frozen at some point while I was connected.
For my host PC:
1) Windows 7 Professional 64bit
2) TeamViewer Version: 7.0.12979
3) I believe I'm using the View Desktop connection, I know I'm not using the transfer files or VPN emulation mode
4) I believe that it is freezing permanently, I don't recall any of my keyboard functions working (caps lock, numlock etc.)
5) When the Host PC freezes I have no control over the computer, ctrl-alt-del doesn't work, alt-f4 doesn't either. I've had to reboot the system each time this has happened
6) I haven't tried closing everything else yet, but will do so the next time I get a chance.
In the mean time, what could possibly be causing this?