We have a large number of custom profile fields and moving them up or down in position using the up and down arrows does not work as expected. Sometimes the field "jumps" many spots lower after clicking the up arrow, for instance. It usually only happens when trying to move a field many spots (so clicking the up arrow several times in a row for instance).
It's also very cumbersome and slow. If possible, replace with the drag and drop interface when for instance reordering Spaces in the admin console.