mythtv build warning

I just built from the Debian source for mythtv 0.25-dmo2. I noticed
this complaint at the end:
dpkg-gencontrol: warning: Depends field of package mythtv-frontend: unknown substitution variable ${python:Depends}

This is in a testing chroot, after
apt-get build-dep mythtv
DEB_BUILD_OPTIONS=nostrip,noopt dpkg-buildpackage -b -uc -D

This just FYI, in case it indicates a bug.
Ross