I thought it's supposed to be "dh_clean"? (yeah I dunno what it's doing either) try to check the clean section of the debian/rules file, maybe change the command there.
#!/usr/bin/make -f export CFLAGS = -g -O$(if $(findstring noopt,$(DEB_BUILD_OPTIONS)),0,2) export V=1 %: dh $@
clean: dh_clean
clean: dh clean