Custom action submenu lost position

Version information

4.21.7-dev-566526fe

Steps to reproduce

1. Edit -> Configure custom actions...
2. Edit a custom action: give it some "Submenu".
3. Then right-click a file to show a context menu with that UCA.

Current behavior

The submenu with that action (looks like a folder) appears at the bottom of the context menu, not in its old place.

Though through "File" Thunar menu the submenu is in its proper place.

Expected outcome

Before the new UCA menu editing, the submenu was at the same place as the action in it.

Therefore the ordering in the context menu is lost, which is inconvenient.