Reviewer team for branch doesn't seem to receive email warnings of merge proposals

We're trying to setup a slightly more social handling of the project, with a bit less friction. To that end:

* A development branch dA was created in general account (team A)
* A second team (B) was created and set as the *reviewer* for branch dA
* Team B's mailing list was activated, team members were subscribed and the list was set as the team's contact address, and tested (it's working)

So far so good, but here's the rub: I expected that merge proposals to dA would result in an email being sent to team B's mailing list (as it's dA's reviewer), but so far *none* of the merge proposals has resulted in any kind of email sent to team B's ML. Likewise when explicitly requiring a (supplementary) review from team B. This means team members are *not* made aware of newly created merge proposals, and usually forget to check the dedicated page (especially as there are few proposals right now, because they take ages to be reviewed, because team members aren't aware there are any).

So what's the issue? Do I have to subscribe team B to branch dA for it to get merge prop emails? And in that case, what the hell's the point of asking for a review, if the tentative reviewer is never made aware that somebody's waiting for him?