The refcount reported for a ghost was one too small, because the code for
ghosts and non-ghosts was the same, and presumably "it's a feature" that
the code for non-ghosts deliberately lies about the true Python refcount,
in order (guessing here) to report what the count would have been if the
cPickleCache didn't exist.  But while the cPickleCache holds on to a real
reference to non-ghost objects, it does not hold a real reference to ghost
objects, so subtracting "an extra" count for all objects made it appear
that non-referenced ghosts exist in the cache (which doesn't actually
happen).

What a tangled web we weave ...