Steps to reproduce

1. load the zul and attached Excel file

   <zk>
   <spreadsheet id="ss" src="/WEB-INF/issue/header-example.xlsx" maxVisibleRows="800" maxVisibleColumns="111" width="50%" 
   		height="100%" 
   		showContextMenu="true" showSheetbar="true" showToolbar="true" showFormulabar="true" 
   		/>
   </zk>
   

2. scroll to right most end quickly
3. scroll to left for 40 columns at least

Actual result

Merges cells are shifted left

Workaround

Scroll to left most end

Debug information

• no javascript error when the issue happens
• reproducing rate 50%, you need to reload and try