Actually for all non-trivial forum, we really need release note for the reason you told. I think even in maintenance release, IPS should say something about the release to inform us of the situation. Important bug fixes list would be nice, and it also show us you are really working on it and we would really improve our site by upgrading.
I understand the technical situation quite well as I have read through the issue report about this.
My point is, most public forum is, you know, public. In my opinion, this behaviour favor minority of the forum while opt out the majority, and does not support the use of sharemedia tag in public forum. Currently, I don't want to educate my user to use that because they'll ask "Why can't we quote the image?" and I have no eligible answer from user's point of view. I'm suggesting that while it's necessary to enforce the permission, this should be configurable in some way for the sake of public forum.
I know it's kind of security enforce, but I believe many forum owners don't really want it that way. Our users always complain that it's annoying because they cannot quote reply to the picture. Should we have the configuration option to enable/disable this?
For the sake of example, here is some random picture.