I am not sure if I am the only one but sometimes I wasn't able to swipe to receive an incoming call. The touch screen just wasn't responding. In fact, I had to press the lock button to turn off the screen and turn it back on before I can swipe to receive the call.
Happens for me as well.. quite a few times.
I thought it was just me, but i guess I have company now

Can you describe the event a little in detail ?
I guess it happens when you pull your phone out of pocket, something related to proximity sensor ? Because, i always house my phone in my jeans & sometime it so happens that i cannot slide & answer the call after removing it from my pocket. I also switch off & switch on the screen & then slide to answer works.