Access is a little weird in that area. The event procedure name has to match the pattern object_event (though you leave off the "On" for the event).
The magic phrase that goes in the event property is [Event Procedure] which tells Access to look for the corresponding procedure with the above formatted name. You can also put the name of a macro or an expression starting with "=" (the later could be a way to call an alternate procedure) in the field.
So it isn't a bug, it's just different.