Originally Posted by
makin'miles
I wonder if miles post depending on how the agent rebooks you in their own system (ie, if they pull a seat from J, or just do something else to upgrade you).
Paid upgrade from original "eligible-to-earn-miles" booking class will give you the mileage in the new (upgraded) class. So for your case, paid upgrade from M to Biz no doubt earns miles in Biz class.