There is a reproducable problem that stops the activation of the out of office (as well as delegation, password change etc.) in fact all the requests passed to the AdminP (there is no AdminP request posted)The reason is that local names.nsf for the user is still in ODS 20 or sometimes ODS 41.
This is due to the DCC (Dynamic Client Configurator) depends heavily on the ODS of the local address book. This can easily happen as the client migration process never takes into account the compacting of local databases (and so upgrading the ODS)