Last modified: 2008-07-07 17:18:27 UTC
When Extension:Configure is installed, diffs are no longer displayed. It then only shows the page content and the edit summary.
It appears to only break revision diffs once a change is actually made with the Configure extension.
fixed in r37266 (version 0.5.1).
You'll need to make a dummy edit on Special:Configure and purge diff cache (if enabled) by calling diffs with action=purge.