Steps to Reproduce

run scroll-flickering.zul

scroll slowly: left - right - left - right ...

Current Result

sometimes the scrollbar flickers to different positions while dragging

Expected Result

non flickering scrollbar

Debug Info

Root Cause

ZK-3588 (draw one more time)
https://github.com/zkoss/zk/blame/3e4c3ce00f52ff2a45006013c24f782c2e008273/zul/src/archive/web/js/zul/mesh/Frozen.js#L427
ZK-4115 (trigger reflow + layout)
https://github.com/zkoss/zk/blame/3e4c3ce00f52ff2a45006013c24f782c2e008273/zul/src/archive/web/js/zul/mesh/Frozen.js#L404

Workaround