I think should be fixed in misc/debian/control.sid. How should it be tested? We already have Debian buildslaves which test the building of .deb's (see the "Debian Waterfall" on the Buildbot), but I guess those two buildslaves have pyasn1 installed, so they failed to detect this bug in control.sid. Could we use some sort of chroot to make sure -- oh, I know! pbuilder is for this. pbuilder is a tool to make sure that your build is not using any Debian packages other than the packages specified in your debian control file.
Created a new ticket (#1256) to be about setting up a pbuilder-managed buildbot step. (Or some other similar tool to pbuilder if you prefer.)