From Blizz forums: "If you have the largest shield on yourself, it wont remove it when you cast it on other targets . If the heals (and thus shields) on other targets are larger than the shield you have on yourself, it will remove it from yourself.The bug happens because of mishandling the preference allowing you to overlap shields on a player and prefer a large shield over a smaller existing shield. You can work around this in pvp once you know a small heal on yourself wont break your shields on other players when you swap to max rank or slower casts."Just in case anyone was wondering what was broken with it.
Thanks, that's definitely the useful information that should have been in the article itself.
I'm sad to say that when I saw "phase 6", my brain first went to pandemic reopening schedules, and I got very confused as to what that meant for WoW...