Software constantly locking the CTRL key

I have been diagnosing this problem for so many months now. At this point, I can safely say that I've ruled out all other software. Here's the issue:

After a bit of painting, SP lags (obviously). After any really rough lag, there is a chance that my CTRL-key will suddenly lock and I lose all control over my computer. To the point where I need to shut down/restart in order to gain back the use of my keyboard.

This is the only program where this problem occurs. I have waded through nine-million useless MS-posts telling me to look at keyboard drivers and other ancillary nonsense that I tried many months ago.

Has anyone else encountered this? I keep my video drivers up to date, but this problem continues to rear its head on the reg. I've rebooted four times today thanks to this.

Thanks in advance.