Cannot use key `space` as shortcut for custom actions

Version information

Thunar 4.18.11 and earlier, Arch Linux

Steps to reproduce

1. Open UCA configurator: menu Edit, Configure custom actions...
2. Click + to create a new custom action
3. In Basic tab, click on the button on the right of Keyboard shortcut:
4. Press key space

Current behavior

The key space is not accepted as shortcut: the dialog to select the shortcut stays opened.

Expected outcome

The key space should be accepted and the dialog closed, like for example if I press <Ctrl>+space or A.

Additional information

There is a workaround to use space as shortcut:

1. create the custom action and use for example <Ctrl>+space as shortcut.
2. close all instances of thunar using thunar -q.
3. manually edit the file ~/.config/Thunar/accels.scm to replace the shortcut of the custom action from "<Primary>space" to "space".
4. restart thunar.

This workaround works, so technically there is no problem to use space as shortcut.

Another interesting point: if I try to modify the shortcuts of "normal" actions (menu Edit, Preferences..., tab Shortcuts):

• some actions, like About, allow the use of shortcut space
• some other actions, like Back does not allow the use of shortcut space