1. (Turn off the 2017 wikitext editor, if relevant.)
2. Go to http://en.wikipedia.org/wiki/Special:PendingChanges and select an article to review. A diff will open.
3. In the second column of the diff, near the other editor's username, click the small 'Edit' link. (Depending upon your preferences, it may say "Edit source".)
4. Look at the buttons below the editing window. The Big Blue Button says "Submit changes" (from [[MediaWiki:Revreview-submitedit]]).
5. Just above the Big Blue Button, tick the box for "Accept this version".
6. On ticking the box, discover that the Big Blue Button switches to say "Save page" from [[MediaWiki:Savearticle]].

It is surprising to have the button's label change mid-edit.

This change doesn't happen in the 2017 wikitext editor. (It's also not possible to reach the tick box to accept the previous changes without first making some change to the article, as the Big Blue Button is grayed out until you type something.)

(First reported by User:Nick Moyes at enwiki)