When TpConnection's status change to CONNECTED, it is re-introspected. That introspection will get supported contact attribute interfaces. If it gets ContactListState SUCCESS before re-introspection finished, supported ifaces could be missing when preparing the TpContact objects and so all features could not be prepared. According to Will, it is fine now to give unsupported ifaces to GetContactAttributes, so I suggest fixing this by just requesting all wanted attributes instead of filtering on supported ones.
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