This design concerns more LG phones, in my case it's LG G2 Mini, but it was reported also on LG D605 Optimus L9 II and probably other LG phones with the same logic.
On the back of LG G2 Mini (Android 4.4.2), there are 2 buttons, which keep being pushed in my pocket.
Unfortunately, there are applications mapped (by manufacturer setting) to the up and down buttons (some drawing notes and camera) when the phone is locked. They keep being launched unwillingly in my pocket.
I've searched through all the settings but couldn't find how to get rid of this mapping and set the buttons' action to void in the phone-locked mode.
My phone is rooted so I can change the system settings but don't know where it is stored.
EDIT: In the official LG upgrade of Android (5.0.2) the problem is solved, see my answer.