Handbrake problem?

Anyone else come across this problem?

Only seems to have started recently. When ripping a DVD through Handbrake, I leave my iMac to get on with it, and as normal, the screen goes to sleep.

However, whenever I wake the computer by clicking the mouse, Handbrake finishes the rip with its normal message " Your Handbrake ...is complete", even though the rip isn't actually finished.

Any ideas folks?

 

I am using Mac OS X 10.8.1, and Handbrake 0.9.8. I also tried using the latest nightly build, but same result.

Of course, you are correct that I can stop my iMac from sleeping as a workaround, (Thank you for that. It really never even crossed my mind), but it seems strange that I have never had this problem before.