Some features are disabled in mute-mode to make sure you will not accidently save, download or comment on a different jamtrack from the one you are currently hearing. You may either lift the mute-mode to download or interact with the currently displayed remix, or move to the currently playing track with the green GOTO button.
Without knowing a track's correct ID you can't share it or you might upload your remix into the wrong place.
And that can be embarassing.
Make sure you get the download you want.
Track ID Numbers on wikiloops