You're rinsing the pasta, and not letting it properly cool
For some reason, human beings have an inherent and unexplainable need to run any food we eat under hot water before we cook it. This is so wrong. Here, at least.
"I have heard that people say to rinse the pasta in the colander with cold water to stop the cooking, but when you do that you are rinsing all of the starch off the pasta. I find this makes the sauce not stick as well and the flavors to not integrate as well with each other. I would recommend after draining the pasta, tossing it with olive oil and then spreading it on a flat surface so it is able to cool that way." -- Aaron Meneghelli, executive chef at Carneros Inn (Napa, California)