@Jdforrester (WMF) or anyone else interested,
Note that while I fixed this template's output (and the other MW beta version templates) so that they don't show bad data, this should really be fixed in the Module code, since Module:Version still manages to construct a nonsense (and broken-unicode) string for things like the git tag/branch/urls, and will still output them if invoked directly:
{{#invoke:Version|get|beta|git}}
=> REL1_�