eg I moderated (hid) a test post. When I go to the diff, I can't see what happened.
http://flow-tests.wmflabs.org/w/index.php?title=Topic:S6awcbng807rvznk&action=compare-post-revisions&topic_newRevision=s8ymcs3q3s9wcfgg
That page should give a summary of the action that took place, if it wasn't a content-edit. It should look like an edit-summary, per usual log items.