Very similar thing happened to me. I had an MBNA CC and a BoA CC from 1998. Somehow I just stopped using the BoA.
Then MBNA was bought by BoA and then the troubles started. I ended up in a payment plan to payoff my MBNA/BoA. It's now reported as closed by consumer with a bunch of lates from 3 years ago. Then after PIF back in January, BoA sent me a card in the mail. I had completely forgotten about my original BoA CC. Called them thinking they had rehabbed my MBNA, no such luck. It was the original BoA card, pays as agreed, but only $500 CL. Not bad, great for history points.