Teams Notifications with Guests

@dazzatrio @Pn1995 StevenCombs  ChrisWebbTech  ChrisHoardMVP 
I have much the same query on this - but perhaps different looking behaviour - namely I have NO red dots.

I have my own company with my own tenancy (call it ABC,) but work full time for another organisation  (DEF) that has just transitioned to Teams from SfB.  I am looking to implement a sort of Support desk for users within my own company where they can post into a Support Channel - but since I need to have the DEF  tenancy using the Desktop Client because it is 10000% more active for Support, I worked out what might be an easy solution, which was create the Channel in ABC teams, invite my DEF External login as a Guest.

Now that actually works and I can easily as some have indicated Switch between seeing My ABC tenancy and the other DEF tenancy Teams with the Dropdown at the top menu.

However I have tested with My ABC user by Adding a comment in the channel, and even doing an @ Mention of my DEF Guest account within that channel (done from another PC with teams Desktop) - Subsequently NO Red Dot, no notification, no "Someone mentioned you in teams" email, etc.  I left it for a little while and nothing - Then I go to the Drop down menu, click on My ABC tenancy and it seems more like it switches accounts at that point, opens up all My Company channels, and Desktop Notifications all of a sudden show up in sequence at the bottom of the screen.  Which seems to mean you can NEVER log into more than one account at once - which we sort of knew already - but even this Guesting functionality should be more fluid than this shouldn't it?

So is this by design - ? or just plain broken?