Share your experience!
My mobile (Xperia mini st15i) has problem with sensor keys as it keep on close application as it starts & gives back to running application what shall be the solution for it.
I suggest that you try to run a software reinstall using SUS.
http://www.sonymobile.com/gb/tools/update-service/
If the problem still remains you should contact your local support team, to have the phone examined and fixed at an repair center.
http://www.sonymobile.com/global-en/support/contact-us/contact-info/
