That's intended behaviour (so far as I'm aware), and not changing. The visibility-* class doesn't refer to the visibility of posts that have the tag, but to the visibility of the tag itself. This equates to the least-restrictive security level at which the tag appears, because if you can see at least one post with that tag then you can see the tag.

Once this patch goes live it will become possible for a layout (or a style layer) to be written to show the extra "split" information of how many times the tag is used at what security level. So somebody could make a style layer that does that. Being fairly new to DW, I'm not sure whether that's a suggestion for dw_suggestions or a request for dw_styles or dreamscapes.