Every single menu is affected. Some buttons like the Hamburger and Overflow menus can be closed if you click on them again, but most others remain permanently open unless you do something that forces menus to close. That includes going into customization for toolbar buttons or selecting an action for the context menu.
Here is a video showing the issue (length is 1:19): https://www.youtube.com/watch?v=hWrGNRS9_24
This does not happen with Chromium, QupZilla or any other Qt or GTK based application.