I've searched but can't find the answer to my problem.

I've set the phone to autolock after 5mins & set a password. What I've noticed is that when the phone was previously left in the phone function e.g. after making a call, & then just letting the phone go into standby mode by itself, when I subsequently wake the phone, it hasn't locked at all.

In all other circumstances it locks just fine. Is that a bug & if so if there a fix or work around.