Steps to Reproduce

run the attached example broken-styles.zul
1. scroll to the bottom of the sheet below row 150
2. scroll up to the top (quite slowly)

Current Result

depending on the scroll speed and row loading position styles below the merged cells break resulting in 0px-height

Expected Result

untouched styles

Root Cause

this is a side effect of ZSS-1117 (and ZSS-1149)

Workaround

apply the attached JS patch patch-merge-cell-style-leak.js

<script src="patch-merge-cell-style-leak.js"/>