A fantastic port of the arcade game I loved to hate. I'm terrible at it, but just find it so difficult not to play. Only one thing, I found this bug during one of my session (see video at the end of my blog entry)....
So... the game has been heavily tested by three different people and this has never happened. Analyzing the code thoroughly I find nothing wrong. Have you tried my original version or one of the cracked ones?
Emulators are programs and as such they can contain bugs. Just see the long list of "Known bugs" on the VICE website. Also, version 3.1 is now a bit old, as they have reached 3.6.