List of steps to reproduce (step by step, including full links if applicable):

• Thank an edit outside the page history using the API.

new mw.Api;
api.postWithEditToken({action:'thank',rev:279988,source:'Test!'});

The revision in the example exists on https://commons.wikimedia.beta.wmflabs.org/wiki/User_talk:AJ-test. The thank arrives, I tested that.

Now go to page history.
What happens?:
( undo | thank )

And when thanking there, the "thank" becomes "thanked". The API returns {"result":{"success":1,"recipient":"AJ-test"}}, but no new thank is delivered.

What should have happened instead?:
I'd expect to see "thanked" on the page history.

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc.:
I could imagine technical restrictions on showing what was thanked on the page history, I must admit that within my script I can also only show the edits you already thanked by using my script to thank them. But I figured the extension would have more extensive access.

Possibly more confusing is the API response. You can run the example over and over on the same revision and it'll always return "success", but it's only actually delivered once.