SUMMARY
The Global Menu widget renders 2 varying menus when activated via keyboard shortcut. This happens with both Qt & GTK apps.

STEPS TO REPRODUCE
1. Place a Global Menu widget. This bug can be reproduced on both panel & desktop.
2. Right-click the widget and select *Configure Global Menu...*
3. Appearance → Enable *Use single button for application menu*
4. Keyboard shortcuts → Set the shortcut, any will do.
5. Open an app with an application menu. e.g. Dolphin
6. Activate the widget with the selected keyboard shortcut. Observe both menu

OBSERVED RESULT
Once the widget has been activated, observe the rendering of 2 menus with varying style & behaviour.
To see the effect more clearly, activate a Global Theme with a transparent background.

EXPECTED RESULT
The widget should behave as if the widget has been clicked by rendering only a single menu.

SOFTWARE/OS VERSIONS
Operating System: Manjaro Linux 
KDE Plasma Version: 5.17.5
KDE Frameworks Version: 5.66.0
Qt Version: 5.14.1
Kernel Version: 5.5.6-1-MANJARO
OS Type: 64-bit

ADDITIONAL INFORMATION
This bug was first posted on Reddit [https://www.reddit.com/r/kde/comments/f9afe7/global_menu_applet_displays_twice_if_triggered/].
Here's the screenshots showing the bug in effect:
1. [https://i.ibb.co/CWzNGt3/kde-global-menu.png]. Notice how there's 2 different menus. Only the menu on the front should be shown.
2. [https://i.ibb.co/6P9Y526/Screenshot-20200307-181607.png]. In this screenshot, the widget is placed on the desktop rather than the panel.

Additionally, a video showing how to reproduce the bug in question have been posted on YouTube [https://youtu.be/ZzH9ZnD7dTI]. In this video, the differing behaviour between both menu are explored.