Steps to reproduce
Change a page's content model (has to be reversible, eg wikitext->javascript)
View the diff (1)
Revert via rollback
On the success screen, view the diff (2)
Undo the rollback, and see the diff (3)
In each scenario, the difference is given as "no difference". Instead, it should be clear that the content model has changed.
I was able to reproduce this issue at mediawiki.org project sandbox. But I still don't get why I was able to "rollback" content model change. It's a log action.
(may be off-topic) Both move and content model change action leaves a null edit in the history. So I tried to revert a move action with rollback and it didn't work as expected. Maybe the bug is "one should not be able to revert a content model change using rollback like the move action"?