While going through Growth-Team's backlog today, I've noticed that one of the tasks, T338174, is somehow in two different columns on the Growth-Team workboard, see task details:

This is also reflected in the Move on Workboard action in the Phabricator dropdown (see that both Triaged and Backlog have the full circle under Growth-Team, which means "the task is here now"):

The workboard also works fine -- the task is present two times there.

This interested me a lot, as I didn't know this was even possible. On my end, the task displays in the two columns in a persistent manner, so this seems to be persistently stored in Phabricator database.

Interestingly, the maniphest.edit API documentation (https://phabricator.wikimedia.org/conduit/method/maniphest.edit/) say under the column transaction type that it can "Move a task to one or more workboard columns.", so this seems to be a supported functionality in some ways. In any case, it doesn't seem to be something that can be triggered via the standard Phabricator UI, only from the API.

I suspect this happened because of some Phabricator bug, as it was not @KStoller-WMF's intention to have this task in multiple columns. To answer that question, I'm filling this task.