Part of this issue I can reproduce. At any time the computer is thinking, exiting the application causes unusual behavior (Easier to notice on settings above World Class where plies >= 3). Sometimes it exits with an error right away; sometimes if you are closing the application when the computer was normally thinking the application won't close but the progress (thinking) bar will continue to move then exit with an error; or the progress bar stop when you close the app, and then exits with an error.

What I haven't been able to see (yet) is a case where the computer was thinking for an excessive amount of time on a regular move that would require using the task manager (or close button) to get out of.

When the computer was thinking too long, how long did you wait before trying to exit (with close button and/or task manager)?

Posted on rec.games.backgammon:

There's a bug in gnu backgammon that has been around for at least the last two major releases, and it is very annoying. The program gets into a state where it will not exit. (MS Windows.) Click on the X button at the top right, and it just goes catatonic. Have to kill it from the task-manager. It happens if and only if the green bar at the bottom-right that goes back and forth when gnubg is "thinking" gets stuck on "think." I have not been able to discover any pattern. Sometimes it happens right away; Sometimes I play for 20 or 30 minutes before it happens.

I am pretty sure it happened on my previous machine, which was a 32 bit with 2 processors. It is doing this now under Windows 7 x64, service pack 1. Four processors, using all four. I installed a pre-built binary from the official download page. I am using a 2D board. Tutor mode ON. Strength set to Grandmaster 3-ply.