dh_ocamldoc strangeness

[Eric Cooper <ecc@cmu.edu>]

I'm converting one of my packages to dh_ocaml 0.9.  It uses cdbs, so
I'm trying to use a debian/libfoo-ocaml-dev.ocamldoc file instead of
specifying OCAML_OCAMLDOC_PACKAGES.

I don't have any special flags to pass, so I tried creating an empty
file.  Here's the weird part:

1. When I use debuild, it seems to work fine.
2. When I use git-buildpackage, none of the API html files get generated.
3. If I use git-buildpackage, but make the .ocamldoc file contain a
   single comment line, it works OK again.

Any idea what's going on here?