[boost] What is http://downloads.sourceforge.net/boost/boost_1_63_0.tar.bz2 ?

The link http://downloads.sourceforge.net/boost/boost_1_63_0.tar.bz2 redirects to http://downloads.sourceforge.net/project/boost/boost/snapshots/master/boost_... which seems to be a snapshot from master, and VERY different to the boost_1_63_0 release (which makes it a VERY misleading URL). How often is that snapshot updated? Shouldn't it have a different name if it's not boost_1_63_0.tar.bz2 but some completely different set of sources (which currently don't even build)? The Fedora Linux packages have been using that URL, for several years by the look of things. So I have no idea what arbitrary collection of changes we've been shipping instead of a proper release.