Why does my S5 disable the screen lock itself?

[Fta Fun]

It has been a couple times I've noticed that there is no need to swipe the pattern lock to unlock the screen even I didn't disable it.
I search to find no thread regarding it.
Does anyone have the similar circumstance?

 

[B. Diddy]

Welcome to Android Central! What's your Automatically Lock interval set to? If it's a long interval (like 5 minutes), that means the phone will wait 5 minutes after the screen has gone off before it locks again. 5 minutes is longer than it seems.