Your solution did not use panels, only one grid and a fixed height.
Not really what I need to implement. So I played around with this for a while, and found the solution:
The trick is to add an extra div around the div containing the grid:
<div id="splitter">
<div>
<div id="leftGrid"></div>
</div>
<div>
<div id="rightGrid"></div>
</div>
</div>
You used that in your solution, but did not explain that this way the key. Hence it took me a while to figure out what the work-around is.
Thanks for your support.