In Avid Studio an issue in exists where, after leaving transition editors such as proDAD Adorage, proDAD VitaScene, and the HFX Editor, background rendering does not occur for the transition. If you want the transition to be rendered for an accurate preview the workaround is to restart Avid Studio. Once it restarts, background rendering for the transition will begin.
Update: This issue should be resolved in the latest patch. Click here to download the Avid Studio update.