Anyone else have leaks with Playtex Insulated Spill-Proof cups???

[momathome]

I have used Playtex sippy cups for 5 years and have never had a problem until now. While the regular cups have been great, the insulated ones have been leaking on me like crazy. No, this is not a valve issue - the leak is coming out of the sides of the lid, not the part where they sip from. I screw on the lid as tight as it can possibly go and then I will go to pick the cup up and milk will start pouring down the sides. It is destroying my diaper bag and I am quite annoyed because these cups were not the cheapest things in the world. Does anyone else have this issue???
-Lauren