I realized that it only happens when you set antialising to 8x and have transparency antialiasing on at the same time or separately. Disable transparency and reduce antialiasing to 4x and the issue is gone.
At least this worked for me.
And don't forget to restart the game after changing the settings too.
EDIT: The bug seems to be back now and the above suggestion does not work. I try different combinations and when I manage to make heraldics look ok, my heavy kuyak goes full transparent this time. Weird issue is weird.
