Re-collapse of combo boxes after items retrieved

When `ComboBoxItemsPopulatedWithoutDropDownOpen` is set to `false`, combo boxes were expanding, but not re-collapsing after their items were retrieved; this caused problems as the first mouse click would be swallowed by the combo box (which would then collapse) rather than the target UI element.

In this pull request I have included two additional UI tests which check the state of the combo box is correctly restored.