graphical glitch due to computation in another thread

Hello (again),

we are having an issue on 2013 model (UE40F7000SL precisely) (seems it does not appear on 2014 model)

while doing some heavy computation (AI for chess) in a separate thread from a CSharp library, the rendering sometimes glitch to black on half of the screen (VBL-related) during a frame.

a short video where we can see the glitch at 0'10 and 0'17. (screen going red while computation is active)
https://www.dropbox.com/s/aajrwy4h05xubhr/video_glitches_during_computation.mp4?dl=0

issue 637192 on fogbugz with video and project sample.

any hints on how to resolve this issue ?
we tried adding some sleep inbetween computations, controlling the thread priority or ownership, nothing fixed the issue so far..

Thx