autoreconf removes config.guess but fails to restore it

[Magnus Fromreide]

Consider a package that uses only autoconf, no automake, libtool or any
such thing.

Further assume that is uses AC_CANONICAL_something so that config.sub
and config.guess are needed.

config.sub and config.guess are manually added to the package as per the
manual.

Now, running 

autoreconf -if

removes config.sub and config.guess but fails to recreate them.

This feels like an autoreconf bug.