Hi Joe,
I was trying to reproduce this in 6.4.0 Release d QA16 (the most recent QA of WinWeb) but was not able to.
I create a new form, added a Button and deployed. Then I used F12 to inspect the Button and observed that font-family is set to Tahoma on that button's span node. Then I changed the Button's and Form's font to Garamond and deployed again, and then I get font-family set to Garamond.
May be that I am using a different version from what you are using, so please elaborate on the exact version used for your test.
Palli