What do you make of this??? I was just offered a promotion, but was told I would take a paycut for it!?

I was just offered a promotion on Monday, but the boss explained that I would have a lull in pay for an uncertain period of time. This is a commission job, and the promotion is commission, but has big payout potential. I stated both my enthusiasm, but concern over the lull in pay, and requested that I could make up the difference working late. Apparently, he didn't like that, says it's a full time job (I'm already working 40 hours!!), and that he has to rethink it. All day, he completed avoided me!! What do you make of this? Was I wrong to be concerned about my pay? I only requested working extra hours for a few weeks, and totally think this is a valid concern....what promotion is a step up, with a decrease in pay? I think he's being totally unreasonable. Your thoughts?