Unable to play an old development card after buying a new one,

I know that you are not allowed to play a dev card on the turn you bought it.
However, in two separate games I was unable to play a dev card bought on a previous turn AFTER I bought a new dev card.
Both times when I tried, the message for "Not allowed to play a dev card on the turn you bought it" came up.
I'm guessing this is a bug.