I have created a simple word-guessing game using Sencha Touch 2.0. I have had multiple people try it out on iPhones and the Kindle fire. The interface has a button for each letter of the alphabet and a toolbar with multiple buttons. On both iPhones and the Fire, the buttons often don't fire the 'tap' event when pressed. On many occasions, I actually see the button show a 'depress' animation when the user presses the button, but the 'tap' event handler is not called. It often seems like the user has to press the button for a second or two, and only then is the 'tap' event handler fired.
In all my development testing (on a Chrome browser), the buttons have always responded very reliably to clicks. I am considering changing the interface to do away with the letter buttons and use the device keyboard instead. I can't do away with the toolbar buttons. Why are the Sencha buttons so much harder to use than native buttons?