We have installed CU's for SharePoint and I've run psconfig to upgrade the environment. After running, the servers list as "No action required" and everything is well. Untill the next day... I checked CA again and the servers are once again listed with "Upgrade Available". Hmm, weird. Ok; ran the command again, same result. Next day: Upgrade Available again.
I checked with stsadm -o localupgradestatus and found out that one particular site collection (a root site collection) is listed because it requires an upgrade. But I don't know why its not being upgraded. Apparantly because of this single site collection, the entire farm is flagged as if it requires an update?