Find any edited post on ee-flow or beta-wiki, click its mini-pencil icon and choose Show changes, every time I get an error:
Error Diff operation can only be done for two revisions belonging to the same post."
I just made and edited (as Selenium user) on Talk:Sandbox the "New post, test edit" post under "New topic, test edit"
The fix for bug 56196 changed query string parameter names from [] to _. If I change the _ back to [], I see the diff fine:
Version: master
Severity: major
URL: http://en.wikipedia.beta.wmflabs.org/w/index.php?title=Talk:Flow&topic_newRevision=051019b8127934b9401d02163e39327f&topic_oldRevision=0509c8092f50eefec58902163e39327f&workflow=0509c8092f3ceefec58902163e39327f&action=compare-revisions