GNOME Bugzilla – Bug 685384
Menus taller than the screen height will overflow scroll and activate an item when clicking to open the menu
Last modified: 2017-08-24 22:42:49 UTC
Created attachment 225679 [details] screencast If you click and release (a normal click) a menu to open it, the item under the mouse cursor gets activated instead of just opening the menu. The attached screencast will explain better than words.
I can confirm this and add that is only happens when the menu is very large and therefore overlapes the menubar. An example is the message menu in Evolution which is very difficult to use on small screens. The main problem is the way large menu's are handled. In my opinion it would be better if the menu's would never overlap the menubar and the scrolling button is presented below the menubar like the menu's in Iceweasel. That way you also avoid that large menu's pop up and block you when you move along the menubar. Bug 675942 seems related.
*** This bug has been marked as a duplicate of bug 675942 ***