Thanks for the replys guys, I wondered about the trough switches because I had an earlier issue there which was causing similar issues but they were completely random last time. This time (so far) it's only happened in the sequence I mentioned above. I've had a day out on this machine today rebuilding flippers, sling shot switches and replacing a few other random switches and lamp holders which were in need of it so haven't gone in to switch test yet. Hopefully I'll have everything ready to test in an hour or so.
If nothing abnormal shows up in switch test, might be worth doing a system reset.
The problem seems to be consistently triggered by a specific sequence of events.
I would think the problem would be more random if something was wrong in the matrix.
Easy to try, just remove/reinstall batteries.(Bye bye highscores!)
By the way, you sure have some cool games. 
Thanks, when they're playing they're great
