Eclipse RCP: Combobox in toolbar gets cut up in Win7

I'm currently trying to specify the size of a combobox that is placed in the toolbar of an eclipse rcp view. The combobox and its functionality works fine - no complains there. It is just the display that开发者_如何学编程 is wonky. Under WinXP everything looks fine, but under Win7 the bottom line of pixels of the combobox (the dark line that is the border) is missing. The combobox extends WorkbenchWindowControlContribution. I've tried to edit the margin of the parentControl and also the layout of the combobox. But so far nothing worked. The vertical size of neither the combobox nor the toolbar seem to be editable. But how do I get a complete combobox?

Or is this maybe a known bug that is unsolvable as of yet?

Thanks in advance

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There is a known issue of the computeWidth not being passed to the WorkbenchWindowControlContribution.