Before people accuse me of being anti-Apple, or crazy, (or both) let me provide my bona-fides. Mac owner since 1993. I've had every iPhone from the original to the 5s (no 5c.) I'm an Apple fan, a Mac guy, ad an iPhone owner. Search for my previous posts here.
I think this has to do with iOS 7. (I don't have an iOS 6 device to compare it against.)
I did this on my 5s, once with my finger, and once with a tablet touch pen that I use when testing application on the Android devices at work.
1)First take off any case you have on your iPhone.
2)Go to the home screen of your springboard.
3)Swipe down to reveal the Search Bar (,this will bring the keyboard out too.)
Here's where I can see the issue:
Attempt to click the "Cancel" button by tapping the right side of the word directly in the middle and baseline, like on the "cel" letters in "Cancel."
Result for me is that the "Cancel" button does not register a press.
I can get it to register a press by clicking in this way:
1)Click on the capital "C" in "Cancel"
2)Clicking the "cel" of "Cancel" just below the letter's baseline but still within the blue bar.
I repeated this same test with a known "good" iPhone 5 and it had the same issue. (It was my old iPhone 5 I sold to a co-worker which had it's touch screen replace in late July.)
Now do this (with the search bar and keyboard still present):
1)Click on the right side of the P button on the keyboard. Aim as far right as you can.
Result:The P registers properly and is shown in the search bar. Type a few more letters for the next step.
2)Click the delete button on the keyboard (which is just above the Search key at the very bottom) and aim for it's outer right edge.
Result for me: It worked sometimes, but not other times.
3)Click on the left side of the "Q" button on the keyboard.
Result: The Q registers properly and is shown in the search bar.
4)Click on the "123" button at the bottom left of the keyboard. Aim as far left as you can by the "1"
Result: The button is triggered sometimes, but not all of the time. (Make sure you have some letters in the search are before performing the next step or the button will not be active.)
5)Try to click the very right edge of the "Search" button, on the "arch" or "rch" letters.
Result: The "Search" button is not triggered most of the time. You can trigger it by clicking on the "S" or to the right of the "S" (but still to the left of the space bar.)
My theory is: I think the software behavior that has the phone attempt to disregard "accidental touches" is suppressing the button pushes when they are near the top and bottom outer edges of the device.
This, combined with iOS 7's new layout styles of placing "buttons" to the very edges is leading to some frustration for some users. The buttons I originally posted about being non-responsive in other apps , such as Music or Nike+ are
Just my thoughts.