Slate viewer closes when trying to click the ComboButton drop down

Slate viewer closes when trying to click the drop down labeled "ComboButton" if the drop down just above it is flickering due to position issues.

1. Open the Slate viewer
2. Drag the Widget Gallery tab down so that it's just above the bottom of the screen
3. Click the drop down that is called "Item A 0"
4. Notice that the dropdown menu begins to flicker
5. While dropdown is flickering try to click the drop down labeled "Combo button"
6. Notice that the slate view closes

Expected: The drop down item lining up the current position of the mouse would be selected or the Combo Button drop down would open
Result: The viewer closes

SMenuAnchor - Assertion failed: NewMenu->GetOwnedWindow().IsValid()