Obviously this isn't a serious bug. Instead of queuing up a number of structures and Not gaining tax benefits for the population commited to structures which are in the building queue but not are yet being built, one can simply build a structure as the current building in the queue empties. This way, if you have say, a 15 turn garden queued on top of a 20 turn temple of essence, and then a 10 turn market, you aren't suffering an artificially reduced tax base for no good reason.

It isn't really a "bug" at all by my definitions - it's just that, the way things got coded, it happens to be more convenient to Not use the convenient queue system, if you're trying to eek the biggest advantage out of your cities and people. Maybe this was actually an intended feature to reflect double-edgedness of bureaucracy. Who knows.

Edit: Either I missed a change to the base taxrate per population point, or I never knew exactly what it was before. Regardless though, after messing around a bit it looks like what I described above isn't actually the case. It just so happened that in a pair of instances I examined, it only appeared to be so because of coincidence and the assumption that a unit of population generated the incorrect amount of gildar as taxes per turn. Sorry!