Ruby workstation? If so, check the keyboard on it. Also check the soft key file and make sure there is not a "stop" key where there is not supposed to be one.
Keyboard cover (keyboard condom). Had a site that had one stretched over the buttons too tight. They hit anything close to the stop button and down they went.
No, I can't sell you cigarettes. I don't work here and this pile of parts is the cash register.
A few years back I had one like this. The only way I could duplicate was by quickly flicking the breaker to the EC. We put a voltage recorder on the AC circuit, didn't find squat. Replaced the entire EC. Never did solve the problem... I left the company and didn't think about it again until now. File this post under the "Not Helpful-Just Sharing" category.
This is my signature. There are others like it but this one is mine.