It's interesting to read the replies and good (I think!?) to see that I am not alone with this issue. I have just had a play in the dome, repeating the problem and have generated two log files (SGP & Dome ASCOM), available here:
It is raining, so I didn't open the shutter. On Park, after the dome had gone to home and back to slave to the mount and then the mount had gone to its park position, I unslaved the dome and sent it to its home position. While it was going to its home position, SGP showed that it was 'NOT RESPONDING' in the title and the blue windows circle loop thingy span. I don't know if that is relevant?
The other thing that I notice is that 'in the olden days', when I clicked Park in SGP, both the mount and the dome would go to their park positions simultaneously. Nowadays the mount stays still until the dome has stopped moving. Again, is this relevant?
I hope that the logs help progress this one.
Thank you all.