For example, type api in the Tags field in the Maniphest edit form. I would expect to see things like MediaWiki-API, RESTBase-API, Parsoid-Web-API, Web-APIs-Hub. Instead the only thing I see is ApiFeatureUsage. This makes tags pretty much useless for people who don't spend a lot of time in Phabricator (and merely annoying for the rest of us).
(The magnifier glass thingie is even more useless: typing api gives me several dozen completely unrelated projects, but still none of the API ones.)
(The dropdown I get when typing something starting with # in a textara works sanely, on the other hand.)