Show Cue System

During a show today, we had scs suddenly jump backwards in the cue list, for no apparent reason.

We played cue 6, and then for no apparent reason it moved backwards, so the next go fired cue 1.5. (I believe the status on screen did update to reflect this, however the operator did not notice in time, and fired the stray cue)

I can't see how this could have occurred apart from possible operator error. I've emailed you details of a tracing version to run so if you can reproduce the error then I should be able to see what causes it.