If gss-proxy holds what appears to be a valid ticket but it turns out to be unusable it should acquire a new ticket.
One scenario is if an IPA master is re-installed, see https://fedorahosted.org/sssd/ticket/2217
Another potential issue (untested by me) if time goes backwards and the ticket is not yet valid.
Deferred to upstream gssapi
Metadata Update from @rcritten: - Issue assigned to simo - Issue set to the milestone: X - DEFERRED
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