Our cups are starting to get a white film on it even after it's been thoroughly cleaned. Once it dries it looks like there is leftover milk in the cup. I called customer service and was told other parents have complained and one parent sent back six cups but they were tested and nothing is wrong with the cups. They are unwilling to send us replacementsEven though they claim nothing is leeching into the cup it's really gross. The funny thing is the newer cups are the ones with the problem not the ones we've had for a while. Have any of you experienced this?