Both the Aztecs and China (or rather Qin Shi Huang) have the ability to rush city construction, either wonders (Qin) or districts (Aztec), using builder charges. Because this production boost comes in fairly large chunks, and because builder charges are often more hammer efficient than direct city production, it often makes sense to rush a district or wonder with builder charges while building something else with the city's actual production. This is especially true for the Aztecs, for whom a district costs exactly 5 builder charges. At present, it's possible to do this, it requires a ton of fiddly micromanagement. If for instance, you want to rush a campus while building a settler, you need to switch the city's production from the settler to the campus, then use the builder charge, the switch production back to the settler. Doing this once isn't much of a hassle, but when you consider that each district takes 5 charges (and that the Aztecs tend to have wide empires), it adds up to a lot of extra clicking. There's really no reason for this sort of micromanagement to be required. If the developers want to allow building one thing with builder charges and another with city production, they should allow builder charges to be expended regardless of whether the district or wonder being rushed is the active item in the "queue". If they don't want to allow this, they should block changing production and using these worker abilities in the same turn. I think my preference would be for the former option, but I'd consider either an improvement on the status quo.