When the Network of Citadels tech finishes researching, units that were already affected by the network will keep the old buff value, only new units entering the aura will benefit from the new attack speed boost. Old units either need to go out then reenter or wait for the aura to go off then on to benefit.
Notice that this is NOT a tooltip bug and I actually tested and measured the attack speed before and after the upgrade (by counting attacks over a long period).
On a side note there is a tooltip bug which I am reporting in another thread.