I have a small test part attached to show this problem.  I am trying to get 10 air holes in this piece. 

Boss-Extrude1/Fill Pattern1 - this should create 10 holes, but it only creates 9.

Sketch 2 - This shows there is clearly room for 10 squares if Boss-Extrude 1.

Boss-Extrude2/Fill Pattern2 - The block has been enlarged to just make room for 11 squares.  In the boss, if you change the vertical dimension to 45.8 (instead of 45.9), the fill pattern will jump down to 9 holes instead of 10.

What gives?

Thanks!