To reproduce:
1. Open any of the menus mentioned below the repro steps
2. Click on some other button
Notice that even though the menu closes, the button doesn't get pressed (see video in edit)

The menus with which this reproduces:
Layout
Layers
Color choser
Reference selector
Animator>parameters>+
The menu with "Maximize, Close Tab, Add Tab" that's on every tab
Clicking on another tab eats a click
Display
Add profiler
Active profiler

This is not an exhaustive list: most drop-down menus exhibit this behaviour
The only one I've found that doesn't is the gizmos menu

Reproduced on: 5.6.0b5, 5.5.0p4, 5.3.6p5