[6039Y] Phone unlocking in pocket...

I have just a simple question to other users of this (otherwise nice) phone: I have the screen lock set up the standard way (no pin or anything), I also use the display doube-tap wake-up gesture (I found it quite useful for the phone with symmetrical front side). What happens is, that if I have my phone in the pocket, display facing the leg, the phone sometimes wakes up itself, runs some application or make a phone call to somebody from my quick dial list. If I position it facing outside of the pocket (which is quite insecure for the glass), it does not happen. The weird thing is, that if I switch off the double-tap feature, it does not solve the problem... The phone is with stock ROM 5.0.2-01003, no root (unfortunately). Does this happen also to anybody else, or just me?

P.S.: I wonder, why there's no such simple feature like "solid phone display lock" when the proximity sensor is covered... Possibly, somebody will implement it in a custom ROM (I hope ;) ).