Share your experience!
My Xperia S stopped rotating its screen whenever i need to go into landscape mode. I have auto rotating screen on. I have tried rebooting and deactivating auto rotation, but nothing happens. This is especially problematic when watching videos or texting.
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/