I would guess the recording was recorded out of phase, and you corrected it. Or something is wired out of phase in your system, and you corrected that.
Many recordings are recorded out of phase, or some instruments in the recording out of phase, so that is why a phase switch can be useful to correct this, if it is important to you.
Many recordings are recorded out of phase, or some instruments in the recording out of phase, so that is why a phase switch can be useful to correct this, if it is important to you.