I don't know if this is a bug, if so it's also on regular game worlds - but I noticed it most here.
I have both building upgrade voucher and instant upgrade voucher, but the building upgrades still cost cash. What is the building upgrade voucher for, if you can't use it to upgrade a building?
The train purchase voucher, for example, allows purchase of the train for zero cash. So why do building upgrades cost cash AND use up a voucher?