Hey E. I think what's happening is you have a yellow pepper with a green immature color that inherited the trait of anthocyanin in the immature pod from the NSR.
The presence of anthocyanin in the immature pod creates a purple color that masks the appearance of green from the chlorophyll. Without additional gene mutations, both the chlorophyll and anthocyanin in the immature pod will degrade as the pod ripens. When both have degraded, the ultimate ripe color is revealed.
If the anthocyanin degrades faster that the chlorophyll, then you'll see a purple immature pod revert to green before the chlorophyll degrades and reveals the ripe color. If they degrade in the opposite order, you'd see a pepper go directly from purple to the ripe color.
Peppers that mature green have a mutation that prevents the chlorophyll from degrading as the pepper ripens and they have a mature color lighter than green, typically yellow, which, even though present in the ripe pepper, is masked by the green of the remaining chlorophyll.
To answer your question, yeah, in my experience that's somewhat unusual. I don't remember seeing a pepper revert from purple to a strong green color prior to ripening - though some do come to mind that transition through more of a cream color. The certain pimenta de neyde derivatives and aji ayuyo come to mind.