I'm not sure about the internals, but when those filters are there, the GPU process causes a lot of CPU load on every frame. So much that it often hits 100% of the single core it uses before it's able to draw at 60 fps. Oh and it redraws the tab bar a lot. It redraws it every time you scroll a page, and it continuously redraws it when there's a tab playing audio in order to animate those waves emanating from the speaker icon. Yes, it redraws the entire tab bar for a 16x16 animated icon.
They unfortunately don't have a public bug tracker.
