A couple years ago in early December I was Christmas shopping in Marshall Field's with my Field's charge which I hadn't used in awhile. I got to my 6th purchase (and was not even close to my limit), and the card was denied. They called Customer Service and until they could talk to me, they weren't going to allow any more charges. Something similar has also happened with my Visa card.
As inconvenient as it can be, I'm grateful to know that the card companies are watching accounts that closely. Now I try to remember to call a credit card company anytime that I'll be using that card outside of my usual pattern.