With the new debriefing window introduced in 0.52, only the title for the relevant end shows up, not the text. For example, in the Headhunters mission, the briefing.html file contains the following:
<h2><a name="Debriefing:End1">Mission successful</a></h2>
Previously, this would display "Mission successful" as the title, with the text "Well done." below it. In the new debriefing window, "Well done." is no longer displayed. This problem affects Escape from Stratis also, as well as 3rd party content that uses the briefing.html file for debriefings.