If this is happening for you and you want to fix it the quickest way do do this is to edit
Ruby Hamil.tmLanguage on Mac OS X this can be found at the following location:
/Library/Application Support/Sublime Text 2/Packages/Rails/Ruby Haml.tmLanguage.
Once you have it open look for the line
<string>sass</string> and delete it.
As soon as you save the document it should no longer associate SASS files as HAML, now this isn't the case the SASS syntax should take over (assuming you have downloaded it).