Hey Chuck - i've been investigating this and I think it might be to do with the order you lay them down in almost as it's inconsistent. Even though the float left and the float right for the 2 component parts are correct,  it allocats nth-child-1 to the item on the right and nth-child-2 to the one on the left, but then at other times it works ok. 

For example I have identical 2 part blocks at the bottom of each page. Feedback links on the left and a next button on the right. On all but 1 of my pages I see the next button come first then the feedback part. On that one page the feedback comes first then the next button!