You shouldn't have asked!

Just to check - is your NavBar sitting in the pop-up Base layer and another "MouseOver "+ Base layer? Base is the name of the layer pair.

If not, the NavBar is in its default MouseOff and MouseOver layers so any activity with its sub-menus automatically moves focus from the roll-over layer back to the default pair and so closes the pop-up layer. (See Help > Search: Layers, Mouseover (Rollover) & Pop-ups)

Having done what I have described, I then tried variations of closing automatically on roll-over and click.
Nothing worked.

I reverted to my usually approach of creating a CSS3 NavBar.

Sorry, on Xara's behalf,
Acorn