I'm sure others have seen this before, but I haven't. I have an award flight for later on this summer that consists of VCE-LHR-PHL on BA and PHL-DCA on US, all on one ticket. The original booking was just the BA flights, since the US stuff wasn't available. Adding the PHL-DCA segment actually dropped the taxes and fees about $10 and change per ticket. The agent couldn't explain whether it was taxes or fees. Seemed odd to me. Just curious, is there an obvious answer I'm missing?