NGC7000 Evo50 w flattener - what is happening in this image?

[vineyard]

Hello,

I was testing out a Starizona EvoFF v2 flattener last night on NGC7000.

Here is a JPG (for file size) - only ABE & HT done in PI (calibration & integration in APP before that).

If you look carefully at the brighter stars towards the left hand edge, there are bright starbursts that trail towards the middle of the edge, and top left hand corner & bottom left hand corner also show a bit of shape deformation - also a little bit on the right hand bottom corner.

Is this just a sign of spacing not being quite right (w perhaps a bit of tilt), or is there something else happening (like pinching) or some other problem w the flattener?  

I'm hoping its not pinching or any other defect (& its not in any of the other stars in the middle of the image) - but I've never seen a starburst like that on just one point of a stellar disc before, hence hoping some more experienced imagers can shed light (if you'll pardon the pun) pls?

Thank you!

Vin