Missing build logs

I'm managing the build of several instances of the same application
via Anthill (it's a web app, and we run both our testing environments
off the same Tomcat instance).  It seems that in my quest to keep my
anthill working directory clean and well-structured, I've lost the
ability to capture the output of my Ant script.

I want to keep all my build directories in a single subdirectory of
anthill.  So my tree looks like this:

C:\anthill
---builds
------dev
------beta

I then point repository.subversion.work.dir to builds\dev for one
instance, and at builds\beta for the other.  I point
anthill.build.script at dev\build.xml and beta\build.xml,
respectively.

When I build my projects, the -rev.log files are appropriately
populated with the Subversion log history since the previous build. 
However, the -build.log files are empty.  0 bytes.  I haven't been
able to try sending email from my desktop Anthill installation due to
configuration of our SMTP host.

Is this a limitation of Anthill, or have I missed something in the
configuration?