I can reproduce the issue.
Set the menubar vertical.
Reload the page.
C...

I can reproduce the issue.

Set the menubar vertical.
Reload the page.
Change the menubar position to horizontal and try to hover on the menu without reloading the screen.
Hover will not work.

However, The given patch failed to apply to me on version 3.4 so I have created a new for it.
Please review.
Thank you.