[NOT A BUG] Guest posting in public groups not working

[hollosch]

I have a public group and set to "Also allow guest posting into news feed…"
But doesn't work. Guests can't post in the news feed:

FERIENSTADT

Ferienstadt Community

regio-portal.wiki

 

[Truonglv]

I have tested and it's work fine. Guest are here is not member of group.