I have a VST plugin set up in Audition CS6 specifically for sidechain compression. During software playback, the effect works perfectly, but it's completely absent on the exported mixdown file.
I emailed the plugin creator in July about the issue and received this response: "The solution to this in other host programs is to select the 'realtime export' option or similar. I'm not sure if Adobe has this feature." A new version of the plugin was recently released, but still has the same problem. I can't find a realtime export option in Audition, but this VST plugin did work properly in Audition 3 before I upgraded to CS6.