Thanks for the response Peter

I never have "allow lead in bars" ticked, in fact every box in that option window is unticked.

If I have "visible metronome 1234" selected then the number "1" is displayed when the first note sounds ie when the problem occurs. If I don't have visible metronome selected then the problem still happens but the number "1" doesn't appear.

The easiest way to demonstrate the problem is to select "pause until midi received" and use the Jukebox on a folder with lots of midi songs. In Jukebox select "preview after 4 bars" and keep pressing the space bar each time a song loads. When I do this about 20% of the songs sound the first note then stop until I start the song with the space bar. If I have "metronome 1234" selected I also see "1" each time it happens.

Thanks
Tony