We will try to reconstruct the same problem locally, meanwhile you can try to change xml as
<afterInit>
<call command="splitAt"><param>2</param></call>
<call command="setColLabel"><param>0</param><param>XXX</param></call>
</afterInit>
As for problem in chrome - please be sure that left and right part of headers have the same number of lines ( so if grid’s header has two lines in right part - left part also must have two lines. If all cells rowspanned in the single line - sizing may be wrong )