I'm really confused about my DS8's WJ III Reading scores. Hopefully, Dottie can help me..... You are still our score expert, Dottie!

I have 2 score reports, one normed based on his grade, and the other based on his age.
Norms based on grade 3.9/ age 8-7
Broad Reading 143 / 142
Letter-Word ID 132 / 134
Reading Fluency 153 / 164
Passage Comp. 129 / 130
Now, how is it possible that while the subtest scores are individually raised, Broad Reading (composite) score is ended up lower? (even though only 1..) I just can't understand.
Any idea?
Thanks.