[palosanto]

Perhaps its only me but my user experience indicates this could be a bug....

1) Chose a setlist
2) Long Press a song: now you can select songs with ticking the checkboxes
3) Select some songs

If by accident you now tap the song number the edit cursor jumps there.
From now on I can no longer tick /untick checkboxes of songs in the setlist to my liking. The edit cursor will stay active in the number field even if I close the keyboard. 
I have to exit the songlist altogether, start from scratch and hope I wont again tap on a song number....

If intended this seems counterintuitive to me...

What device are you using?

It works as intended in my Onyx Max Lumi.
Clicking on the number allows you to reorder that song to whatever number you enter.  
You don't have to have any songs selected to change the numbers, this is independent of long-pressing and selecting or unselecting boxes.
Also, even though the number is now selected I still can tick/untick other songs without a problem.