organic group forum restricts viewing forum nodes by group membership

This is the default behave that works smoothly unless you may want to have a generic container for users that did not join to any groups. What happen is that building a container from the default /admin/content/forum interface and after you add a forum
this forum cannot be used because if you go to the forum URL and try to add a topic the requested Forum dropdown list of
"-Please choose-" from the Forum* list do not allow to choose any. It's blocked.

Is there a workaround?
Any suggestion very much appreciate.