I haven't seen anything about this anywhere else on this forum or on Google, and I think it's an oversight that slipped through with 4.3.
If you are attuned to a raid that has either a clickable (like BWL) or an NPC to talk with to teleport you inside (like MC), those methods of teleportation will put you into the raid without being in a group. It's not really a huge deal since you could just invite another person normally and use the portal, but this is slightly more convenient. Walking through the instance portals still requires that you be in a raid group though.