I'm calling this a design bug.
The log in my group shows that a member changed to Special Notices, and afterwards, changed to Following Only. I believe she thought that the second change would result in her following individual messages. But instead, the Special Notices took precedence and she is not receiving any regular group messages.
It seems that Special Notices should be in a separate category from the choices Individual Email, Digest, and Daily Summary, all of which do provide access to individual messages but in the latter two cases, in a summarized format. Instead, Special Notices is grouped together with those three choices even though it's a different kind of restriction. I don't think it makes sense to allow Following Only simultaneously with Special Notices only, because in the normal course of events, members would not follow topics designated as Special Notices.
Worse, a member can do what my group member did this morning - namely, change to Special Notices and then think they are changing their mind by selecting Following Only - but instead, the Special Notices restriction remains and she now receives no regular group messages.
Messages are the sole opinion of the author, especially the fishy ones.