Ah okay. That’s true if the author wanted to say this in a more general way. 
However…
(the nitpicker goes on…)
… this bug report (“it did not used my own private key”) refers to the LE client, because other (currently not existent) ACME clients obviously do not have to have this bug.
And it’s also no bug in the protocol, but in the client implementation (of this specific client), so IMHO it’s clearly better to say “LE client” here.
Edit: Don’t ask me why smileys like (:smile:) are now displayed in black/white style…
Test: 
If you cannot see this here is the image it shows: 