While not common, there are some packages that set different versions for some of its subpackages. (Notable examples of this are musescore, pandoc, perl, perl-Encode, ruby, and texlive/texlive-base.) When built with build-rpms-local, a subsequent build-rpms-local or build-container-local lists the version of the package as a whole based on the version of the last subpackage therein rather than that of the SRPM, which (if the subpackage version is less, which seems to happen in these cases) then makes it think that the local build is outdated and act accordingly.

--allow-outdated is a workaround in the meantime, but it would be helpful to fix this properly.