Am i the only one?

Or does anybody else has this problem with COD4. When i push down on the left analog stick and move up to sprint, the character doessprint for awhile but without releasing it, it just automatically at times resumes to walking on its own. And it can get frustrating at times, since i will find myself pressing the left analog stick several times especially when u need to get the hell out of somewhere nad not being able to do so as quick as i would want to. Should i believe that my wireless controller is faulty or is this normal? Any light on this would be appreciated.