Please, either take abbreviations or don't. I typed out Burlington Northern Santa Fe and it didn't take it. It takes BNSF. I typed UP, but it insists on Union Pacific. Be consistent.
While I agree that abbreviations should be accepted, technically they are not wrong here. The official legal name of the UP is Union Pacific, while the official legal name of the BNSF is... BNSF. While BNSF was originally an abbreviation for Burlington Northern Santa Fe, BNSF is no longer an abbreviation, but the official name of the railroad.