Weighting works inconsistently

For the most part, weighting works fine, and things alphabetize by default.

However, for cleanliness, what I was trying to do was weight items so that all parents were above child. Like:

P
> P
> P
> P
>C
> P
> C
> C

This *almost* works. I have about a hundred terms, with varying amounts of nesting, and multiple hierarchies at times. In almost every case, I can get all but 1 of the parents above (using negative numbers) the children terms, but there is inevitable one child term that insists on being just above the lowest parent. This is true even if the Child has a weight of 10 and the parent has a weight of -10. No other terms seem to be affected. The child term that shows up is *not* the child that is next alphabetically - it's somewhat random, I haven't found a pattern to it.