There are a lot of similar anecdotes in this thread, but I'm still skeptical. I've had similar issues with my Brother printer randomly not accepting a new toner cartridge and telling me that it's empty. It happened twice. In one case, I had to use some obscure button combination to force it to reset and then everything was fine. In another case, I needed to remove and reseat the cart a dozen times before it suddenly worked.

Anyway, it's definitely possible that these newer issues are Brother doing something nefarious, but I could also see a lot of these issues being with finicky sensors.