I'm having the same problem with a Yiynova drawing monitor. I know it's not a stuck shift key because it only happens with the pen and not the mouse. Alt-Tab did nothing, restarting (both the program and the whole computer/monitor) does nothing. The only thing that had any affect was swapping the "coordinate" setting from Absolute to Relative and back and that only worked for about 5 seconds before going back to drawing straight lines again.
Also, I'm on 1.8.4.693 if that makes a difference. Looks like this issue still hasn't been fixed and none of the proposed solutions worked in my case.
Anyone have any other suggestions?
