When the new Hook system was implemented, hook names with colons were replace with underscores.
E.g. onContribsPager::reallyDoQuery to onContribsPager__reallyDoQuery.
It seems expected, that if an extension has a hook registered in the old format, calling setTemporaryHook() on the hook in the new format should still override the hook. This behavior does not occur as it stands and should be implemented.