moved up and moved down down ones, If I select Menu, from Button

Hi Isomarphic,
I am using Smart Gwt-4.0p version.
I my application, a list grid having a "IMenuButton" in one column. When ever I click the "IMenuButton", a menu will be displayed.
If list grid having less records there is noproblem, but,
if the list grid having huge records(more than 15), when ever I click IMenuButton, menu will be displayed, but the entire screen will be moved up and moved down down ones.
I added IMneuButton to list grid using list grid record component.
Please give me a solution for this issue.
Please find the sample screen shot for reference.

Thanks..!

Attached Images

ListGridHavinghugerecords.png (35.0 KB)