iPhone 5 cases

So, I bought my iPhone 5 and got it a plastic Marc Jacobs case and for some reason calls started to drop and my WiFi signal wasn't very good. I decided to change my case to a Speck (which is still plastic) and now everything works fine. My calls don't drop anymore and my WiFi works perfectly.

Has this happened to any of you?

If so, why do you think it is?

I'm curious...