Many thanks for your reply & yes you get my point(s) exactly. I agree with your comments. I've checked through the SGP & ASCOM logs including the one for my dome. The only explanation for SGP capturing a plate solve image is because SGP did not initiated the scope slew\flip & therefore is 'unaware' of what's taking place at that moment in time.
After further study I'm pretty sure the settings for my Meridian limits are the cause of the unexpected mount behaviour and that's down to my failure to undestand them properly. I thought I had it nailed but I'll try Don's suggestion next time there's a clear night. Perhaps then it will make sense to me.
I agree MFlips are painful and a 'flipless' GEM is a fairly new innovation. It is a GEM by nature of it's construction but you want it to track past the Meridian(s) as if it were a fork mount. I have asked Dan previously about having the track-past & limits as an option so as you comment hopefully in a future release?
By the way congratulations on writing your dome driver. I hadn't written any ASCOM device specific code before either. A few ASCOM client apps but not a driver so hats off to you as there's a learning curve for sure.