Pete,
1 second doesn't really give time to account for bad seeing.
You may get odd shaped stars because the autoguiding program is chasing what it thinks is star movement. It is actually following atmospheric disturbances.
I use 2 seconds on good seeing nights, and 3 seconds if it is below average. This gives the 'star movement' from bad seeing time to average out a bit. The autoguider is happy with these settings and gives me round stars.
I did try it on 1 second once in medium seeing conditions and I ended up with blurred stars.
Also watch the Aggresiveness levels. Too much and the mount will jerk, not enough and it is too slow to respond and keep up. I use Guidedog and keep the aggressiveness around 80.
I don't know what the scale is in PHD.