Yekke2: It’s B’feirush in the Achronim that the Bracha Acharona ends the Bracha Rishona. There is a Machlokes Achronim about if you accidentally made a Bracha Acharona and still have a few bites left to eat. The Magen Avraham says that you may finish eating, and everyone else attacks him for it. (Interestingly, though, many Achronim quote him as saying that you may lick the crumbs off your lips without a new Bracha Rishonah, which Lich’ora is him L’Shitaso that they rejected.) Everyone agrees though that an intentional Bracha Acharona ends the Rishona.
It is Greirah. Greirah happens whenever you have one Bracha Chal on two or more items. As long as you start eating the first, the Bracha continues onto whatever else you will eat. But you have to start eating the other ones also. If you didn’t start eating the rice, the Bracha never “split” into following the rice also.
LU: Al HaMichya only Patters rice Bedieved and because of a combination of Kulos based on Safek Brachos. Mei’Ikar HaDin, it really doesn’t, and therefore there is no reason to tack on Chumros (i.e. that the Al HaMichya ends your Bracha Rishona on the rice) onto this Safek Brachos Shittah.
PAA: That’s cute Drush, but not Halachically relevant at all (nice to see you again, but I expected more substance and less fluff from your return).