I've read numerous posts about iPhone 4 users' proximity sensors not activating when the phone is placed against their face, which has happened to me as well, however I'm also having an issue where it's not de-activating when I pull it away from my face. For example, I will be having a conversation with someone and I'll pull the phone away from my face (to put the caller on speaker, on hold, etc.) and the screen will remain blank like it's still against my cheek. This has happened to me about 4 or 5 times and the screen doesn't reappear until the other party hangs up the phone. Has this happened to anyone else?