When I leave the background image (which is CSS background-position-fixed) flashes as the browser is trying to re-do it dynamically.

Anyone experienced anything like this in the Opera (v. 11.51)?

It creates a kind of funky strobe disc.
Although not desired.

It seems that the image is too large (DPI / resolution) or not cached.

Browsers have to redo the image pixel by pixel in each movement, (the method of operating system is the paint ()) and if the picture is complex, it takes time to re-calculate all the pixels.