Yeah, not sure why this is causing such a freak out. Is this not standard A/B testing? Maybe A/B testing user agent isn't the best differentiator, but at my current gig, we've considered pushing a pricing difference based on Mac vs PC as Apple products are more of a Luxury device compared to the average PC.
It could even be a persistent fingerprint issue. Perhaps their A/B system is fingerprinting, and the two browsers are consistently fingerprinting in such a way as to produce a more deterministic split.
The market will pay what the market will bear, so if you don't like the higher price, then don't buy. Game the system and shop for the lower price if you want to drive the price lower.