Can't use "Users can see topics posted by other users?"

When the setting "Users can see topics posted by other users?" is disabled (to create a private mod/admin only forum for the end user) the following error is displayed for the end-user AFTER posting a thread in the subforum.

"[[Template forums/front/index/forumRow is throwing an error. This theme may be out of date. Run the support tool in the AdminCP to restore the default theme.]]"

The subforum also vanishes for the end user.

This affects both beta 5 and beta 6.