Why would there be?
See, I'm not doing what a lot of people here are doing. I'm not saying "This is how time works, and why this is or isn't a paradox". What I'm doing is pointing out that everyone who does that is following a basic assumption that time must at some point or another return to a linear mode, just as we see it. There is no reason to make this assumption. The only reason that people do is because that is the only way that we are able to conceive of time as existing. Anything other than linear time is something that we can only tolerate as specific, one-shot events. It's part and parcel of living in the 3rd dimension.
Let's look at this a different way: Right now, we are 3rd dimensional creatures trying to wrap our minds around the 4th dimension. Let's take it down a notch and try to imagine a 2nd dimensional creature trying to figure out the 3rd dimension.
In the 2nd dimension, there is no up or down. Let's say we have a piece of paper and a magic pencil. On that paper, our 2D man is walking along, happily humming to himself. Now, we draw a circle on the paper, and within that circle, we draw a star. Our subject arrives at the circle and, after walking along it's perimeter, determines that it is indeed a circle, and not just a wall.
Now, to our 2d subject, there is no possible way to determine if there is anything within the circle. It is, in every way, shape, and form, impossible, despite what some of the other 2d people say about mysterious abilities and psychic gifts that allow them to view beyond. The only way that our subject could possibly determine what was inside the circle would be for us to cut a hole in the wall with out magic eraser and give him a way in. Indeed, if someone told him there was a star in the circle, and then we gave him the ability to see the star, he would find it utterly astounding, and either believe it to be a hoax or a miracle.
But if our 2d subject was of a philosophical bent, or had studied 2dimensional physics, he might ponder what he would be able to do if traveled to the 3rd dimension. What if he could step beyond his 2dimensional existence, and move to a 3rd dimension, where he would actually be able to see things beyond walls, by looking at them in a manner no one else could? Well, it would be an interesting intellectual experiment, sure, but there would be a paradox. After all, if he was able to know what was inside the circle, he would have no need to look in the circle, and thus his reason for going to the 3rd dimension would be negated. Similarly, how could he look inside the circle if the circle never existed, because circles only exist in the 2nd dimension, not the 3rd?
To our subject, living in a 2nd dimensional world, trying to wrap his head around a 3rd dimension would be almost impossible, and he would be tempted at every turn to fall back into his 2 dimensional experience. The idea that there is another entire universe full of people who have absolutely no problem living in the 3rd dimension, and for whom the impossible ability to look within a closed circle is not even a second thought, is quite difficult to grasp.
We think it is a paradox that we can affect the past without affecting the present. Our subject believes that it is a paradox to be able to see within something that is unseeable. We keep falling back into the idea that, once the trip is over, the time stream will return to a linear flow, and we will have to deal with the consequences. Our subject believes that once he returns to his dimension, the inside of the circle will once again be unknowable. It is, ultimately, a matter of perspective. Trying to figure out the logic of another dimension is rather a matter of futility. What we view as a paradox of time is likely no more difficult to those who exist in the 4th dimension as looking within a circle is to us.