In order to achieve the desired behavior, you need to apply some additional styles to the Menu's parent Pane. For example set a "menuPane" CSS class to the corresponding <div> and then use:
The overflow style will allow the Menu dropdown to expand outside the pane's boundaries. Normally panes are scrollable or do not allow overflowing at all.
The z-index style will allow the dropdown to appear on top of adjacent panes and splitbars, by moving the Menu pane to a higher stacking context. Otherwise the Menu dropdown will expand below all next panes.
The zoom style is required to fix an IE7 rendering bug, at least on my side. If you don't support this browser, remove the style.
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