I'm really wondering if the blame shouldn't be put on Scalar::Util instead. That module can be installed both in an XS version, or in a Pure Perl version. And refaddr won't be there, if the latter is the case.

So, blame the fact that Scalar::Util Pure Perl and Scalar::Util XS use the same module name and version number (they actually get installed from the same distro) and no obvious way to distinhuish between them.