Polycarbonate & cr39 lenses

I have had 2 pair of glasses, regular and tinted, for years. They both had polycarbonate lenses and I saw the same through both sets of glasses. I got a stronger prescription recently and got my regular glasses in the same polycarbonate but got a CR39 for my tinted glasses because they said they could tint them darker. But I see a world of difference through the two pair of lenses now. The CR39 magnifies things much more than the polycarb and makes the ground look like it is 2 feet closer to me. The optician has checked both pair in the prescription checking machine and swears that the prescription is the same in both pair of glasses. Does this sound plausible that I would have very different vision when looking through a polycarb versus a CR39 lens with the same prescription? Is my only solution to throw away the lenses in one set of glasses and buy new lenses so that I have the same material in both glasses?

Thanks,
RLC