iPhone 4 Loses All Contacts over night?

My iphone 4 iOS 5.1.1 mysteriously managed to erase all my contacts completely of it's own accord.

I am at a complete loss to explain how a device manages to erase all contacts with out any apparent reason.

The device was connected to iTunes and a device backup made on the 07 Feb 2013 prior to updating a

handful of purchased applications. No iOS update was done because I prefer maps that work such as the

old google maps with iOS 5.1.1. It is important to note that I do also do not use iCloud or wifi sync.

Upon completion all was well with the phone and the contacts were intact.

I turned the phone off last night (12 Feb 2013) upon retiring.

This morning I turn my phone on with no unusual behavior being observed. I come to make a phone call only to

discover that all my contacts have been erased? This is some six days after I connected to iTunes and backed up.

No problem, a minor inconvenience I shall restore my contacts from the backup I made six days earlier.

I fireup iTunes connect my iPhone and it proceeds to auto sync as it has always done. I go to restore my backup

from the 07 Feb 2013 and it is not there. I discover that it has also been erased/over written by the latest iTunes

auto sync process.

Bit late Apple support, to advise people against leaving 'auto sync on' when iTunes install's with 'auto sync on' set as default.

Apple it would be good to know why the contacts are being mysteriously deleted on the iPhone???