Menus will not occupy available screen space

I have some toolbars with menus that are large. Now, when I click on the link to a large menu, often the menu will not use all of the available screen space. Instead, it pops up smaller, with a vertical scrollbar. I have placed no limits on its vertical size.

Why won't menus occupy all the available screen space and avoid scrollbars?

Please can you post the screenshot?

Screenshot. Only about half of the lower pink menu shows up. It has scrollbars.