sometimes there can be some little pellets of not-mixed One-Step in the butt of your bottles if you use the improper amount. Honestly, I have moved completely away from One-step to Idophor and Oxi Clean. I also clean/ sanitize my bottles in the dishwasher before I bottle, its crazy easy and leaves nothing behind. I recommend it.
I put mine upside down in the cases with the bottom lined in paper towels, let them sit while i get everything ready for racking, this allows for most of the liquid to drain out with out getting the bottom of your cardboard cases wet.
I was tipped off to the dishwasher thing on this site. I used it for the last two bottling sessions and it works great. I have always used bleach solution for sanitizing so I rinse the bottles with hot water and stick them in the DW then run the DW without soap. I speed it along by turning the knob ahead while I am getting things ready. Plus now I bottle on the open DW door and never have a mess to clean up from spillage.