Except it they didn't, did they? I don't remember it ever being fixed, they always turned back into farmers/laborers.
Anyway, I'm hoping mobilising in V2 won't convert entire pops, just shave 3k segments off them to form into brigades. So if you have, say, a 30 brigade mobilisation pool it'll take 3000 men from 30 different large pops rather than converting one 90k pop.