That's been the policy for 2 years now.  Credits you purchase for the year automatically expire at the end of the year.  Printing or e-filing any return during the year, whether for the current or prior years, will cost you a credit from your account (which will not show any balance from a prior year).

If you have any returns you're working on and can't yet finalize before the end of the year but still have credits left on your account, you should always print a copy to trigger a "purchase" before your credits expire.  This way, you can print or e-file them later without having credits deducted from you account in a subsequent year.  I also posted a reminder to peer users late last year but you probably didn't notice.