ADDITIONAL SYSTEM INFORMATION :
Windows 10 19041.1
Ubuntu 18.04.3 LTS (in WSL 2)
Openjdk 13.0.1

A DESCRIPTION OF THE PROBLEM :
When using Java inside WSL 2 to execute JavaFX applications (VcXsrv is installed on Windows), after opening a menu in menubar, there is some gap between the menu and the menu bar, and the menu disappears when you release the mouse.

Screenshot: https://i.loli.net/2020/01/13/Wd27McuqSRw4ibe.png


FREQUENCY : always