Consider the following spec:

{{%bcond_without bootstrap

Name: reproducer-dist
Version: 0
Release: 0%{?dist}
Summary: ...
License: MIT
BuildArch: noarch

%description
...

%prep

%build

%install

%check

%files
}}

And a SRPM produced like this (roughly the equivalent of centpkg srpm):

rpmbuild --define 'dist .el8' -bs reproducer-dist.spec

When I build it in c8s-candiate:

koji --profile stream build --scratch c8s-candidate ~/rpmbuild/SRPMS/reproducer-dist-0-0.el8.src.rpm

I get:

https://kojihub.stream.centos.org/koji/taskinfo?taskID=3307787

GenericError: Downloaded rpm https://kojihub.stream.centos.org/kojifiles/work/tasks/7789/3307789/reproducer-dist-0-0.el8%{__bootstrap}.src.rpm is corrupted:
rpm's header can't be extracted: 5 (rpm error: error reading package header)

This works correctly in c9s-candidate.

This problem also impacts real builds from distgit, see e.g. https://kojihub.stream.centos.org/koji/taskinfo?taskID=3310953 for an actual failure.