UIView animations completion block firing when an other animation begins

Question

I use the block base API for my animations on iOS.

One animation has a completion block and that block is called at the end of the animation, nice.

However, that animation can be fired multiple times when the user scrolls (the animation is on a UITableViewCell). When that happens the the completion block is called multiple times. The finished parameter of the block is always YES.

Since the animation is not actually finished (an other animation took place) I thought that the finished parameter would be NO, but it's not.

Did I miss something? How can I avoid the completion block to be called multiple times?