Tonight I ran into a problem with PHD losing the calibration data after a meridian flip. Given the recent changes to PHD/SGP communication I thought it best to post here first.
I started PHD separate from SGP and restored calibration data from a previous session. I then started the sequence and everthing ran normally. The auto meridian flip was triggered around 10:05pm and the flip, auto center and resume PHD appeared to complete as normal. However it was obvious to me that the mount was not receiving guide commands.
What I observed was PHD reporting that it was guiding in the lower left corner complete with the green box etc, but there was no reported error in guiding in the bottom info bar and thus no guide commands were being sent to the mount. Not knowing what else to do I stopped the sequence, closed and restarted PHD and restored the calibration data from a previous session and restarted guiding. Same thing, PHD reports guiding but no guide error or commands being sent to the mount.
So then I closed both PHD and SGP and started completely over. After restoring the calibration data again still the same problem, so I re-ran calibration and immediately guiding resumed properly. It seemed obvious to me that somehow the former calibration data was missing or something, and running a new calibration solved the problem.