ID 485334 - Add Layer dropdown menu can disappear on Linux

Problem summary
Add Layer dropdown menu can disappear on Linux

Customer reported version
Modo 15.0v1

Customer reported platform
CentOS 8

Steps to reproduce

1) Open the Add Layer dropdown menu

2) Open the Enhance:modo Textures or Render Outputs submenus

3) Move the cursor downwards through the submenu

Expected behaviour
The menu should stay open while the cursor hovers above it.

Actual behaviour
The menu disappears.

Workaround
Unknown.

Reproduced by support
This bug has been reproduced in:
Modo 15.1v1 - CentOS 7.7
Modo 15.0v1 - CentOS 7.7 - regression

Unable to reproduce bug in:
Modo 14.2v2 - CentOS 7.7

Earliest version tested
Modo 14.2v2 - This issue doesn't appear in this version and has regressed.