At first, i thought that a click on a menu item wasn't registered properly, but the cause is something completely different:

Open chromium or thunderbird
right click on the window-titlebar to display the context menu
Target the last entry 'close' with the mouse, but move/traverse slowly through the available items from top to bottom. The important part is, that the submenu 'more actions' opens. (don't select anything from here)

Move the mouse further on to the 'close' entry and hold it (don't move any further, don't click)
The desired effect is, that the end of the mouse motion is earlier than the closing of the 'more actions' submenu

The last entry 'close' is seen to be highlighted, but when the submenu closes, the highlighting of the 'close' entry disappears as well.
You need to move the mouse a bit to re-highlight again.

The thing is, this happens also when operated quickly giving you the impression that clicking on the close entry is not registered. That's annoying at best :-)