www for subdomain

I have tried every kind of configuration possible and I cannot get the following to work:

I have a main domain and a subdomain, but ONE SINGLE SITE, not multisite

mydomain.com
subdomain.mydomain.com

With everything set up as per the instructions I can visit subdomain.mydomain.com and i can see my site ok, but if i click a Drupal internal menu item, for example a link which points to:

/mypath

it tries to go to:

www.subdomain.mydomain.com/mypath (with the www)

which results in page not found.

If i manually enter into the browser :

subdomain.mydomain.com/mypath (without the www)

This works.

I have tried uncommenting the lines in .htaccess to redirect to the NON www site - this results in the main domain redirection to non-www but the subdomain still has www.

I have tried adding the non-www code to .htaccess listed here: https://drupal.org/node/1358644 - same result as above

I have tried turning on the www prefix handling in advanced settings as described here: https://drupal.org/node/1121614#advsettings - same result as above

No matter what i do the subdomain always has the www and results in page not found.

Any ideas?