Did you go straight from 10mg dose down to 7.5mg? If so, that was much too big a reduction in one go. What is your reduction schedule? Sometimes the flares will happen anyway, even with great care.

One thing a lot of us seem to forget is that prednisone does not cure PMR. If we get to a certain dosage level and flare, it likely means we have reduced below our lowest effective dose and the PMR is still active.