Flats over-correction with ASI 1600 ?

[maxbob]

 

Hi, I use an ASI 1600 MM cool Pro CMOS camera.  On a 16-bit scale (65550 total adu output) I try to keep my Flat adu to about 1/3 of total, or about 20,00 - 24,000 adu.  I understand that this will keep the flats in the linear range of the camera's response.  Sometimes however,  my flats will leave white-ish motes instead of the dark motes that I would have if no flats were used.  I usually use 30 single flats to integrate into a flat master in PI.
This issue has happened twice now with my Ha filter.

Question:
1. Has anyone seen this before ?, and
2. Is the fix to lower the adu read out for the individual flats to say 15,000 adu.

Thanks for your comments.
Bob

[Astrobug]

Try to use a bias, it could help

[Laurin Dave]

are you calibrating with matched darks? ( which you need to with this camera)  And what exposures are you using ..  following advice I read on CN  ie use between 0.1 and 2 seconds and put a delay in between subs of 10 seconds.. never fails, I target similar ADU