Does anyone have a preference or know of a sonic differnce between
bouncing a stereo track to disk vs a dual mono track?

I usually mix back into ProTools and then take thos files to mastering,
but I bounce to disk for CD-Rs. I did a single test and bouncing two
mono tracks sounded significanly better to me. In fact, I'm wondering
if I somehow made a mistake when I was bouncing and didn't do the
comparison right.
Is there a reason that there would be any difference?