Hey Hans,
Perhaps we should erase all other components that uses IRQs from the system. There is one thread here in the forum, where they had problems with the uart in this case, but I did not find it again.
I tried the system on friday, but hadn't the time to reply. Same as you, I am out and and do much on the weekends. Hope your concert went well. So I think the system flickers one frame, but then stops. It is very short and I can't see it every time. I thought about, what would happen, if there is a FrameBuffer after the FrameReader. The Buffer could repeat the Image when it's buffer runs out, so there will be a way to see what it shows in the first frame. I have not tried that, but it might be interesting. Problem there will be, that the FrameReader and FrameBuffer must share the ddr ram for this.
I will not have much time next week, but perhaps you find out something more. Good luck!