Build failure on Ubuntu: "Debian revision (`ea') doesn't contain any digits"

[Jesse Glick]

Building the Jigsaw forest (updated as of today) on Ubuntu 10.04 fails for me after half an hour with

....
Creating module file jdk.jre at 8-ea.jmod for jdk.jre
....
	done
Creating binary Debian package for jdk.boot
Failed to create package dpkg-deb - error: Debian revision (`ea') doesn't contain any digits
....
Creating binary Debian package for jdk.jre
Failed to create package dpkg-deb - error: Debian revision (`ea') doesn't contain any digits
make[2]: *** [deb-pkgs] Error 1
make[2]: Leaving directory `.../jigsaw/jdk/make'
make[1]: *** [jdk-build] Error 2
make[1]: Leaving directory `.../jigsaw'
make: *** [build_product_image] Error 2

Some bug in jpkg, or in the makefile invoking it?