iMapMyRun Users: iPhone App - Locking the phone??

I have the iPhone + app. Paid for it, love it. But I need a definitive answer, how does the phone locking work? It seemed to fully lock it self on my run today, I had to press the home button and swipe to unlock and it was still tracking perfectly. I just tried a small test where I started a run then locked the phone using the top lock button. I pressed the home button then swiped to unlock the phone and it was working fine.  Once and for all, can anyone tell me how the lock function works on the iPhone + app?