If I understand correctly, this is a problem in plugin openmediavault-remotedesktop? I can not fix that myself?! And it will take even longer before it's fixed?!
Kind of. I can't get xrdp working on a system even without the plugin. So, I don't know what the plugin needs to do to fix the config produced by the xrdp package itself. I will try to look at this soon but I installed x2go on my Linux desktop at home because of this. It works well but I don't like the x2go client.