Metronome Icon Lit But Not Sound

If the metronome was enabled i.e. sound playing and then you switch back to the Cue / Loop section, when clicking back on the Grid tab the metronome icon is highlighted but doesn't sound. You have to click it off and then on again.

This also occurs when loading a track and the metronome is already enabled. There is no metronome sound even though the icon is illuminated.