rpmbuild does not do expand with %if %with(...)

Description of problem:

Sometimes rpmbuild do does not do expand with %if %with(...)

Version-Release number of selected component (if applicable):

rpm-build-4.4.2.3-18.el5

How reproducible:

100%

Steps to Reproduce:
1. cat > test.spec
# for testing
%bcond_without alternatives
%{!?_extension:%define _extension .gz}
Name: test
Version: 1.0
Release: 1%{?dist}
Summary: Just a test
Group: Testing
License: BSD
BuildRoot: %{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id_u} -n)
%description
Just a Joke
%prep
true
%build
true
%install
rm -rf $RPM_BUILD_ROOT
install -d $RPM_BUILD_ROOT%{_infodir}
#%if %{?with_alternatives:1}%{!?with_alternatives:0}
%if %with(alternatives)
echo ft | gzip > $RPM_BUILD_ROOT%{_infodir}/gperf-ace.info%{_extension}
%endif
%clean
rm -rf $RPM_BUILD_ROOT
%files
%defattr(-,root,root,-)
%doc
%{_infodir}/gperf-ace.info%{_extension}
%changelog

2. rpmbuild -bb test.spec

Actual results:
error: File not found: /var/tmp/test-1.0-1.el5-root-root/usr/share/info/gperf-ace.info%{_extension}

Expected results:
rpmbuild expand the correct result: /var/tmp/test-1.0-1.el5-root-root/usr/share/info/gperf-ace.info.gz

Additional info:

replace '%if %with(alternatives)' with '%if %{?with_alternatives:1}%{!?with_alternatives:0}' could temporaryly fix this proble.

replace '%if %with(alternatives)' with '%if %{?with_alternatives:1}%{!?with_alternatives:0}' could temporaryly fix this problem.

replace '%{!?_extension:%define _extension .gz}' with '%{!?_extension:%global _extension .gz}' could temporaryly fix this problem.

There's a indeed a bug here but it's not what you think it is...
Macros are scoped so the _extension %define only exists in the {} block of this line:
%{!?_extension:%define _extension .gz}

Or rather, it's *supposed* to only exist in that block, but due to an ages old bug in the macro engine, it doesn't get undefined until you call a (possibly completely unrelated) parametrized macro, %with() in this case.

This is the correct way, not a workaround:
%{!?_extension:%global _extension .gz}

WONTFIX for RHEL 5 to avoid unnecessary breakage there, but fixed upstream now to enforce use of %global in such cases.