This task refers only to tags applied via API/scripts (as contrary to manually editing them by means of interface elements such as the //Edit tags of selected revisions// button on history pages). Steps taken on test.wikipedia.org:
# Edit some page through the API specifying a `tags` parameter with any [[ https://test.wikipedia.org/wiki/Special:Tags | existing tag ]] (//Applied manually...//), let's say `description`. I used Special:ApiSandbox to perform an edit on [[ https://test.wikipedia.org/wiki/User:Peter_Bowman/misc | this page ]] with the mentioned tag.
# Go to [[ https://test.wikipedia.org/wiki/Special:RecentChanges | Special:RecentChanges ]] and check that your edit doesn't show as tagged. You can see there both of my untagged edits on 24th May. The [[ https://test.wikipedia.org/w/index.php?title=Special:RecentChanges&tagfilter=description | filtered view ]] doesn't show them either.
# Go to the history view of the edited page. The revision should be correctly tagged there ([[ https://test.wikipedia.org/w/index.php?title=User:Peter_Bowman/misc&action=history | my test page ]]), as well as in your contribs page. The corresponding //Tagged changes// counter on [[ https://test.wikipedia.org/wiki/Special:Tags | Special:Tags ]] has been incremented, too.
I have first spotted this issue on pl.wiktionary.org. The last registered tagged edits with the only tag available for manual/per script applying (named `Skrypt`) occured on [[ https://pl.wiktionary.org/w/index.php?title=Specjalna:Ostatnie_zmiany&tagfilter=script&uselang=en | early 23th May ]] (CET zone), although actually those weren't the last revisions to be tagged as it can be seen in [[ https://pl.wiktionary.org/w/index.php?title=Specjalna:Wk%C5%82ad&offset=20150525000000&limit=35&tagfilter=script&contribs=user&target=Zuiarra&uselang=en | this contribs list ]].