Nav Menu doesnt show Title Attribute on tooltip

I’ve shortened my navigation labels to prevent word-wrap on long titles, and put the full title into the title attribute field. I expected the attribute content to appear on the tool-tip when you hover over a menu item, but you only see the nav label repeated.

My site is https://renaissancealive.com

Under the Publications submenu,
the first item is History/Biography: England
The submenu under this shows Historical Documents as the first item, with the same text on the tool-tip. What I put into the Title Attribute was A Collection of Historical Documents – that’s what I expected to come up as the tool-tip