It seems that unless you use the default Windows 7 font of Segoe UI for menubars and menus, these things will not render with the correct window metrics.

Here is an example using the Diamond skin, but with an alternate font specified. Note how menubar items are squished together, dropdown menu items overlap each other or even get cropped. If a large font is used, even weirder things happen.

Is there a way to avoid this with custom skin fonts?

Edit: The fix was to change the "skin defined system-wide fonts" to match the fonts specified elsewhere in the skin. This is just a guess, but it appears Windowblinds was rendering with the correct font, but using the metrics of the system-wide fonts instead. Now that the two match, everything is drawing nicely.