Comment 20 for bug 140964

I'll try to sum things up:

Currently pbuilder-dist calls pbuilder with --mirror $archive and --othermirror $mirror $components
with $archive being archive.u.c or ftp.d.o, and $components being main restricted (universe multiverse) or main (contrib non-free).
As you can see, we don't specify the components for the mirror specified in --mirror. pbuilder uses for that the $COMPONENTS var defined in pbuilderrc.
If this var contains restricted|universe|multiverse, pbuilder-dist will fail with Debian. So the workaround is to put only main in that var and let --othermirror manage the components. That is not the best solution because it's not very clean, and you will get a "duplicate mirror" warning for the main component.

Now the real solution. It's to not use --othermirror (we only want to use one mirror), but only --mirror. But we need to be able to specify the components for that mirror. And here comes the pbuilder patch which adds the --components option. pbuilder-dist will call pbuilder with --mirror $archive and --components $components.

I don't see any other solution to cleanly fix this bug, and IMO "that won't be backportable" is not a good reason for not fixing a bug.