sub menus opening other sub menus sometimes disappear

When using the new context menus on Linux, sometimes opening a child menu that is itself a child menu will cause the current menu to disappear. This may need to be done a few times to get the repro.

Repro:

1. Create a Unity project
2. Repeat the following steps until repro (could be 5+ times)
3. In the project view, click on the "+" button to add an asset
4. Hover over "Text Core" > "Font Asset" (on 2023.2 it is "Text" > "Font Asset")

Result: Every few tries, the context menu containing "Font Asset" closes, leaving only the child menu of "Font Asset".

Expected: All 3 menus stay open

Alternate Repro:

1. Create a Unity project
2. From the package manager, add the "2D" feature
3. Repeat the following steps until repro (could be 5+ times)
4. In the Hierarchy window, right click.
5. Hover over "2D Object" > "Sprites"

Result: Every few tries, the context menu containing "Sprites" closes, leaving only the child menu of "Sprites". And it often pops somewhere unexpected. The original menu also stays open.

Expected: All 3 menus stay open

 

Environment: Ubuntu 20.04 (x11). Does not repro on Mac / Windows.