Doublebuffering synchronization problems when moving images

This is a Quick application, running alone on the display. When I have a lot of images on the screen and move one of them (elevator effect) then this image visually stutters as if I see the framebuffers in wrong order on the display. The effect is triggered by an external button (read via serial line) and when I release that button the image should be hidden. What happens is that the image is hidden but shows up at least once again and then is really gone. The effect persists when I use greater values for FB_MULTI_BUFFER environment variable, just the timing changes.

I have videos that show the behavior, but they are quite large so I can't upload them directly.

My basic setup as shown in the picture:

•  64 images, 135x135 pixels each on the left (static)
• 1 image at the bottom 480x270, chaning contents every 3 seconds, C++ changes a property that has the source filename
• one image that moves (the blue arrow right of the center)

Please see the attached code for 2 ways I tried to get that effect working, both show the same behavior. If I reduce the number of images the problem mostly disappears.