This isn't new.

When they originally started the service, they'd have a site-wide daily buying limit and as soon as it was hit nobody could enter new buy orders.

It got particularly bad during the spring of last year, so much so that people would create bots that you could run that would retry your order very 10 seconds until it finally went through.

I think it was last summer sometime they changed the system so that if they ran out of coins they could guarantee a price on (presumably, this would have been when they ran out of USD on Bitstamp to buy coins with) that you'd get the opportunity to buy but without a guaranteed exchange rate.