On occasion, my Droid Bionic (4.0.4 Ice Cream Sandwich) does not react to screen touches when the phone is ringing. The swipe to answer icon appears, but does not respond. After the call goes to voice mail, I can turn the screen off and back on and the phone behaves normally.
I believe this has only happened when the phone has been locked with the screen off when the call arrived.
I don't receive a large number of calls on this device, so I don't have a very large sample size, but it probably happens less than 1 time in 20. The most recent was within a few hours of rebooting the phone, so I don't think it is due to memory consumption by another app, etc.