Very carefully - and I mean extremely carefully - word it so that it describes what it does, while implying what it should do without confirming that it actually does that.
Also helps if you fix the bug or change the behavior, the docs are still technically correct. I'm only partially kidding, I swear I've seen this a million times in documentation I read.
Hardware Engineers: "None. We'll fix it in firmware."
Firmware Engineers: "None. We'll fix it in software."
Software Engineers: "None. We'll document it in the manual."
Technical Writers: "None. The user can figure it out." etc.