Pop, didn't you see the rolling banner about this a few weeks back? In a nutshell, this is how the new softeware works, it's 100% out of Admin hands about this Group joining deal, it's built into the new software... I know it's a PITA, but whaddya gonna do, right?
... the previous version was so tired and busted it was FUBAR... it's a one-time thing to simply Join, and it's done... Nothing to do with Vendors support, favoritism or anything like that... I believe it's set up so that vendors can have more direct control over their sections, so maybe that's why so much of the default stuff is set differently than before....
You're hip to this stuff, and you know "changes" grind some peoples gears, but it cannot be helped... If Alerts, Push notifications and all that jazz are not acting normal, or you want them stopped, I'm figuring folks will have to check through their Preferences, etc. and make sure things are set as they like,..... Could be this all new gig didn't translate over all the settings as they were before....