Bug 141535

Yep, macro expansion is entirely context free, macros are
expanded in comments, within quotes, on the false branch
of %if tests, everywhere.

Try escaping the % with anothe % to disable the expansion, like
   # %%{some_macro}

Escaping % in a comment by adding another %% is a bad way to handle
this.  Often times I want to give an example %define within the
comment.  That means I would have to write it as %%define, and then
turn around and add a disclaimer saying that my example will not work
because you have to remove the first %.  It sort of defeats the
purpose of the documentation to start with.  Ex - 

# To define your own macro here, so something like
#       %%define cfg_localstatedir /var/tmp
# But be sure to ignore the first "%" above.  I can't show
# the real syntax because rpm's macro processor would mistakenly
# process the %define in this comment.  OH CR*P!  My explanation
# just triggered another error in rpmbuild!

(NOTE: This will indeed cause rpmbuild to fail.)

Even the /usr/lib/rpm/macros file that defines most of the macros used
by rpmbuild allows this sort of documentation:

<snip>
# The configure macro does the following:
#       optionally change to a subdirectory (not implemented).
#       attempt to update config.guess and config.sub.
#       run configure with correct prefix, platform, and CFLAGS.
#       optionally restore current directory (not implemented).
# The configure macro should be invoked as %configure (rather than
%{configure})
# because the rest of the arguments will be expanded using %*.
#
# This is the version of %configure used through rpm-3.0.4.
#%configure     \
#  %{?__libtoolize:[ -f configure.in ] && %{__libtoolize} --copy
--force} \
#  CFLAGS="%{optflags}" ./configure %{_target_platform}
--prefix=%{_prefix}
#
#------------------------------------------------------------------------------
# This is an improved version of %configure (from PLD team).
%configure \
  CFLAGS="${CFLAGS:-%optflags}" ; export CFLAGS ; \
  CXXFLAGS="${CXXFLAGS:-%optflags}" ; export CXXFLAGS ; \
  FFLAGS="${FFLAGS:-%optflags}" ; export FFLAGS ; \
  ./configure --host=%{_host} --build=%{_build} \\\
        --target=%{_target_platform} \\\
        --program-prefix=%{?_program_prefix} \\\
        --prefix=%{_prefix} \\\
        --exec-prefix=%{_exec_prefix} \\\
        --bindir=%{_bindir} \\\
        --sbindir=%{_sbindir} \\\
        --sysconfdir=%{_sysconfdir} \\\
        --datadir=%{_datadir} \\\
        --includedir=%{_includedir} \\\
        --libdir=%{_libdir} \\\
        --libexecdir=%{_libexecdir} \\\
        --localstatedir=%{_localstatedir} \\\
        --sharedstatedir=%{_sharedstatedir} \\\
        --mandir=%{_mandir} \\\
        --infodir=%{_infodir}

</snip>

See how nice it is to be able to adequately comment the definitions?

If you can provide even one instance of where this might be useful in
any sort of typical circumstance, I will happily concede :-)  I
haven't been able to find a good explanation for this behavior in the
other three previous bugzilla postings on this matter.

But other than that, the whole rpm concept has been great and I think
that the spec files are quite powerfule and flexible.  (And I am
serious about that!)