It is an issue with the newest version of google now. It seems most people i have talked to have multiple text clients on their phone like standard Text Messaging app, GoSMS, or google voice but not one hundred percent sure if that has anything to do with it. I know mine does it on all of my devices including a Motorola Razr MAXX, Motrola Razr HD, and a Samsung Galaxy S3.
It is the latest update of Google Now/Google Search that is causing this problem which began in early/mid august and is still unresolved by google(they claim they are aware and looking into the issue at this time) however temporarily reverting to an older version by uninstalling the update will temporarily fix the issue untill google can figure this out.