This was mentioned quite recently.
If I remember correctly, and accurately made sense of whichever prossie was waffling about it (Dani, I believe), then it's a trick they pull were they sort of accept the booking, but protect themselves from negative feedback.
Unlike what Sarah says (
), they tend to tick confirmed
after the event i.e. when they can be reasonably sure you're not going to leave them negative feedback.
If they cancel on you at the last minute? Hey presto, the booking was never confirmed anyway!