I have seen this happen. There's nothing wrong, just a lot of growth hormones making themselves known. I have a tree which has also done this and it's quite an unusual sight ! Mother nature is always surprising us.
Suzy

Thanks Suzy. I was worried, since I didn't buy this from a nursery that maybe this was a sign that a) it wasn't a clematis or b) something was very wrong. I appreciate the feedback.

Laura, your SAC should flower around September-Oct. If not, then perhaps it's another interesting vine. If you can't wait until September to find out what you have, you can post a picture of the leaves and that should make for pretty easy identification.
Suzy