Why is FreeTDS not reading its configuration file when run through unixODBC?

Question

I'm trying to use FreeTDS's ODBC driver to access a MS SQL Server 2005 instance from a Linux application.

When I run tsql on the command line, it will read /etc/freetds.conf and $HOME/.freetds.conf and pull in the options I want to set (confirmed with strace watching open/access calls).

However when I use FreeTDS via unixODBC (which is my real goal) it loads neither file (also confirmed with strace).

Here is my unixODBC config (from odbcinst.ini):

   [Sql Server]
   Description=FreeTDS
   Driver=/usr/lib64/libtdsodbc.so
   Setup=/usr/lib64/libtdsodbc.so

(I also tried without the Setup= line, which is how the unixODBC docs show it; no difference)

What's going wrong?

I'm using FreeTDS 0.82 and unixODBC 2.3.0.