Just so you know, you can't change the title of a thread, a mod has to do it. Changing the title by editing your post only changes the subject of your first post.
ANYWAY! lol. Check to see if the button is actually working everytime you press it. Press it when the phone is not on a call and make sure it takes you to the call history. Press the "End" button and repeat the process several times. If it works everytime then the button is probably not faulty and It is most likely an OS bug, Try reloading the OS or install a leak. Hope this helps!