It does not appear that the mute articulation works properly whatsoever.
Open blank score.
Select trumpet instrument.
Place tied notes for trumpet.
Apply mute articulation to all notes.
Expected: Trumpet changes to mute channel for all notes.
Actual: Trumpet does not change to mute channel for the first note, and ceases to play for the others.
There's a dialog that can be brought up for the mute articulation that mentions the channel playback and such, but it does not appear to be possible to do anything whatsoever on this menu.
The open articulation likely suffers from these bugs as well.