[pmrid (Peter)]

I'm trying to traqck down the cause of slight distortions in the stars I';m getting lately. The attached images are all of NGC2259. OK. I didn't intend to image that item. I was looking for 2359 but set the autopilot and went to bed for 4 hours and - well, you know what I mean.
Anyway, the problem is there and I'd appreciate help solving it.
The scope is an 8" Newt that has previously provided terrific images. It's on a pier and has been aligned and collimated to within an inch of it's life. Tracking was with an OAG and a QHY5 into the ST4 of the EQ6 mount. Tracking was spot on throughout. These images are from 4 hours with a QHY8 with 20 minute subs, darks subtracted and just stretched with PS. The QHY8 was fitted with a MPCC and a QHY8 spacer adapter for it (courtesty of Peter Tan).
The images are TL,TR,BL,BR,C as in top, bottom, left, right and centre. Also a full-frame and a crop of NGC2259 just to prove it was actually there.
The distortions are obvious enough.
Any suggestions?

Peter