The sizing must be terrible from boot to boot. I received my usual size 10 pair as a gift and they were huge. After trying some similar style 9's in store, still muck brand just different sole, I had the the tens exchanged online for 9's. When they arrived one boot was at least a whole size smaller than the other.
I ordered a pair of mucks last year around this time through a similar sale. They fit great and worked well for about two months... then the material cracked around the toe where it flexes and created pinhole leaks in the same place on both boots. Apparently the quality has gone down the tube since they sold out to the Rocky brand.