CSS3 Transition not working in Chrome anymore
Your problem is that you are trying to animate from an undefined property: you are changing left to 239px, but don't explicitly specify it as 0 initially. It therefore defaults to auto, a value for which there is no valid smooth transition to 239px.
Add left:0 to the base definition and you will be fine.
See a JSfiddle here demonstrating your problem in Chrome 32+.