Looking for a solution to this.
On ST3, I start typing a CSS property (i.e backimage) and the correct autocompletion lists shows, but when I press tab it inserts the :; (ie backimage: without completing the css property (background-image:. However, this procedure works as expected in ST2.
edit further investigation, I took @ctruetts advice. Disabled "emmet" package and the autocompletion worked as expected