Thanks, it took a bit of chasing but having the time helped a lot.
The position, sidereal time and pointing state are all consistent and I can see that the mount has tracked past the meridian about 5 minutes earlier.
I can see the driver getting the set side of pier command at 00:58:58.
The slew takes place and I can see the position changing and the slewing state remaining at true until 00:59:52, nearly a minute later. The pointing state has now changed as expected but it does not change when the slew starts, it reflects the mount state and changes when that changes.
What I think may be happening is that SGP is sending the set pier side command and immediately reading the pointing state. The slew is still in progress, in fact barely started so the pointing state has not changed. It changes when the mount state changes at 00:59:10.
@Ken, it looks to me as if you should wait for the set side of pier slew to complete before checking the pointing state.
Chris