Last night, after dropping a package from a control file, I was wondering why my package.install file for the remaining package seemed to be ignored (upstream installs a bunch of stuff that I don't want installed in the Debian package; the symptom was all that junk was making its way into the package). Turns out it comes down to the following logic in CDBS:
ifeq ($(words $(DEB_ALL_PACKAGES)),1)
DEB_DESTDIR = $(CURDIR)/debian/$(strip $(DEB_ALL_PACKAGES))/
else
DEB_DESTDIR = $(CURDIR)/debian/tmp/
endif
i.e. if there is only one package, then by default install in debian/package. Therefore whatever make install does is what you end up with in your package. Although I can see the reasoning behind this, it wasn't what I wanted since I need the package installed into a temporary location (i.e. debian/tmp) which then uses a .install file to pull out only those files I want. The solution is simple, override DEB_DESTDIR to $(CURDIR)/debian/tmp/ in rules.
I hope this saves someone the half hour or so I spent investigating why my install file was "corrupt"!