Because I have done so many, visually you can see whether the barlines line up. And the Player function has its own logic in order to work but you might be able to use this as an additional check device.
Hey dflat -- you've highlighted the issue perfectly. It's newcomers who haven't done so many who are most likely to come up with the user interface shortcomings. Those who have used it the longest are least likely to see them, since they've found the workarounds and won't try the obvious things.

Thanks for your open mind and listening!

Cheers,
Steve