One of the newest entries on the late breaking news article for EV 8 SP 4 (http://seer.entsupport.symantec.com/docs/350361.htm) is an issue relating to opening archived items with the 8 SP 4 client when you have those items in Vault Cache.
The issue that the item doesn't get pulled from your Vault Cache, it's downloaded on the fly from the EV server.
This of course has a couple of side effects notably :-
* Load on the EV server
* Inability to open the item, when you have no connectivity to the EV server.
The good news is that this is fixed now along with a few other issues described in : http://seer.entsupport.symantec.com/docs/354789.htm