== Steps to reproduce ==
1. Create a comment pasting `F270656`
2. Create another comment pasting `F270656`
== What happens ==
{F284706, size=full}
> Action With No Effect
> One of your actions has no effect:
>
> Transaction (of type "core:file") has no effect.
>
> Apply remaining actions?
== What should happen instead ==
No weird confirmation message.
== Why that happens ==
It seems this source code generates the "file reference":
https://we.phorge.it/source/phorge/browse/master/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php;ac99285c57a06ed5699b69242fd6588edd950112$2288-2291
Probably, if file is already attached, it tries to generate a duplicated file reference.