Karbonn Titanium S1 Plus - switches off when the phone is in pocket while travelling

I Have bought this phone few days back.

Features : http://www.themobileindian.com/handset-guide/details/Karbonn-Titanium-S1-Plus

Performance is good.
But the only issue is whenever I am travelling in bus or in motorcycle keeping the phone in my shirt or jeans pocket it turns...

Karbonn Titanium S1 Plus - switches off when the phone is in pocket while travelling