Normally when you inherit a class, and override any of the methods, you call the base method, just to be sure you do not interfere with the inner workings of the class. There is a bug however in the SPItemEventReceiver class that always changes the Status to Continue, even if I decided it should stop and cancel. TMHI this is simply a bug. Especially since the SPEventReceiverStatus.Continue enum value is 0 and thus the default value.
If you decide to Cancel the action do not call the base implementation.
Just a short note to self. A lot of Microsoft applications use WebDAV. If you encounter some very slow WebDAV performance, just disable the “Automatically detect settings” in IE.
Tools –> Internet options –> Connections –> LAN Settings
Speeds up performance 10 times in my case.