I think there's a non-zero chance that scalpers are watching the list of available ticket blocks, comparing frequently to find when a block becomes unavailable (because it's in a cart), and then monitoring and automatically buying any "missing" ticket blocks as soon as they reappear. That's what I would do, anyways.

That said, I would not be surprised in the least if this was being aided by ticketmaster or they were straight up doing it themselves. I just think there is a possible explanation where they are ignorant rather than malicious.