Hi Wichert, I'm wondering about your bug report because the "make distclean" in the clean target of ntop does remove config.cache & friends. The only problem I can see is if you abort the build process while configure runs: There's no Makefile so "make distclean" fails, but config.cache & friends are already present. But this seems to be a general problem with packages using autoconf.
cu, Adrian -- A "No" uttered from deepest conviction is better and greater than a "Yes" merely uttered to please, or what is worse, to avoid trouble. -- Mahatma Ghandi