Hover on main menu causes following item to disappear if spills over to two lines

Created by: mvl22

If there are too many main menu items for the current screen width, and the menu spills to two lines, a hover on the final item on the top line causes the following item to disappear.

Example 1:

Initial state:

Hover state:

(Note that 'Innovation at Cambridge' has now disappeared.)

Example 2:

Initial state:

Hover state:

(Note that 'Contacts' has now disappeared, and an extra blank line's worth of space has appeared.)