Memoir not Obeying Lower Margins

Question

I am using the memoir class to typeset my thesis, with the following commands to specify the margins

\setulmarginsandblock{1.5in}{1in}{*}  %% 1.5in upper margin, 1in lower margin
\setlrmarginsandblock{1.5in}{1in}{*}
\setheaderspaces{1in}{*}{*}
\checkandfixthelayout

and I declare the document class using

\documentclass[oneside,letterpaper,12pt,oldfontcommands]{memoir}

When I run Latex, I get the following output

******************************************************
Stock height and width: 794.96999pt by 614.295pt
Top and edge trims: 0pt and 0pt
Page height and width: 794.96999pt by 614.295pt
Text height and width: 621pt by 433pt
Spine and edge margins: 108.405pt and 72.26999pt
Upper and lower margins: 108.405pt and 65.56499pt
Headheight and headsep: 14.5pt and 21.63501pt
...

The lower margin, 65.56499pt, converts to 0.91in, and the resulting pdf shows the margin to be a little less than 1in. I don't understand why the margin isn't being set at exactly 1in. The other margins appear to be fine. Even if I directly specify the lower margin to be 72pt, it still ends up as 65.5pt.

Answer 1

Changing the \checkandfixthelayout algorithm, as daleif suggested, took care of the problem. In ended up using \checkandfixthelayout[fixed], which is described in the "Laying out the page" section in the manual.