Is this behavior normal for lock screen and Phone app for android 4.1.2? Is this the normal behavior for the LOCK SCREEN?

Scenario

When on Phone app, after disconnecting the call.


Tap on Call button again
Mean while Screen times out, and device shows lock screen (for fraction of seconds)
But, skips the lock screen and shows the phone app again.


Basically it is like skipping the lock screen without passcode. 

Device: Samsung Galaxy Note2, 4.1.2 Jellybean, with the latest update of 'XXDMC3'.
Observed this scenario before and after this particular update is installed.

Edit:

My intention here is to know why some times the default 'Phone' app bypasses the LOCK SCreen.  In the scenario I mentioned, when I again tap on the call button, The screen timeout should be calculated from that instance of time. But that doesn't happen.
Depending on your ROM, there might be two settings for screen lock:


user turns of screen explicitly (default: lock immediately)
screen turns off by timeout (default: lock after 5 seconds if not switched on again by user before that)


You might wish to check with your device. It's usually found in Settings&rarr;Display. Not that this is not separately configurable on all devices.