Format of reference changes in text

I’m using RefMan 12 and using Cite as you write, inserting my references in the Harvard style.  When I insert the reference for the first time it appears correctly in the text: Author. et al year.  However when i insert the same reference a second time in the same document, it inserts it with all the authors into the text.  I cannot find a way to stop this happening.  can anyone help?