Steps to reproduce

1. use MarkerClusterer
2. Optional: use vector maps with fractional zoom and animated cluster markers to see the effect even more
3. clusters get rerendered when zooming even when they havent changed, this causes minor flickering for default maps, but really bad experience if you use fractional zoom vector maps and animated clusters

Video examples

Video example with vector maps, fractional zoom and animated clusters (lots of unnecessary rerendering and animating)

Video example with vector maps, fractional zoom and non-animated clusters (flickering)

Video example without fractional zoom and animated clusters (sometimes unnecessary rerendering and animating)

PR

I am creating a PR for this myself, the fix seems pretty straightforward at first glance.