backward transformer

I have a large transformer that came out of a 48 volt power supply. It
has three output leads, the two center taps are hooked together, the
voltage reads 37.5 from center to either side and 72 end to end. however
when I hook up a 25 amp 250 volt bridge rectifier it reads 33.5 volts
center to end and 67.5 volts end to end. I thought the rectifier would
increase the voltage by 1.44. why is it going backwards?