It seems that the mutliper buildings do weird things to the pop count.
Try deleting any of the following in the above save and see how much the used pop changes a school, merchant or granary.
The amount varies depending on the city in Oxford (capital tech city) they give back 70 pop each
I also had a town hall in an earlier game do a samilar thing.
The studies and workshops show increased cost when buying them but only changed the pop used by 4 and 3.
