This is a bit confusing to explain but I will do my best. I recently upgraded from 16.04 to 16.10 and the behavior of my menu bar has changed slightly.
So before when I would click on a menu drop down option (lets say "File") it would drop down and give me a bunch of options. I could then hover over an adjacent drop down (lets say "Edit") and it would change the focus of the drop down menu. So just by hovering over "Edit" after I already had File open the "edit" drop down would display.
Since I upgraded I can open a menu fine by clicking on it but once it is open hovering over adjacent menu options no longer will automatically open it. I don't know if this was an intentional change with the upgrade but I prefer the original functionality.
If anyone knows how to change this back to it's original functionality it would be much appreciated.
Using the above image as an example, now that "File" is open when I hover over "Edit" I expect it to open automatically but it no longer does.