We've sorted out the details off-list (thanks also to Assaf), and I have
completed the conversion. The attached file 'broken' is the list of all
the tags that I regenerated. If you have an existing clone, git will
not replace your local broken tags by default, but you can fix your
local side by:
$ git tag -d $(cat broken)
$ git fetch origin --tags
then, optionally use git prune to remove the now-dangling broken tags.
I'll leave this bug open just a bit longer, until we have undone the
temporary changes that we had to make to bypass normal tag deletion
prevention.