I think the rationale for the inverted behaviour might be that the spin buttons are placed right next to a dropdown list of possible instruments, and they reflect the order of items in that list. The default "previous / next instrument" shortcuts work the same way. I agree it's inconsistent in some way, though.

I see... personally I would like to have it coherent too, so when I click on "up", I'm used to an increment of that figure or element. Would be nice to see it in one of the next updates in some time, although it's not really mandatory since it's just a small cosmetic touch, and I use the dropdown list directly either way or chose the instrument in the instrument tab.

Changed in r6730.