You sure aren't alone Harmy, it is this difficult for everyone it seems.
Me and DJ got the exact same problem and had to offset this using a script when rendering our projects.
If you can't find a way to fix it, I'll help you when the time comes to make a script for your final encode.
Like:
1. Render an uncompressed avi.
2. Use a script to encode it for blu-ray/mkv which fixes the colorspace.
Or maybe there's some way to offset it in AE?