So a privacy card you used for one merchant was denied by another merchant? And it wasn't due to them rejecting prepaid cards, setting your card to single-use, or setting too low of a dollar limit?
Not OP, but yep, my cards have been locked to the merchant.
I've only experienced this with Kickstarter and then a secondary payment collector (BackerKit, etc) where some extra charge had to be finalized, typically shipping or maybe I threw in some extra doodad, and then had it fail because that second charge wasn't technically the same merchant.
But this was fine and I was happy - working exactly as intended. I just created a new privacy card and updated payment.