You're right the adjustments and changes are applied to the library as they are made.
Is this something that just started happening or is this a new Aperture installation?
If it has just started happening and nothing else has changed on your system then you should start with the Aperture 3:Troubleshooting Basics. I'd specifically look at doing a permission repair and library rebuild.
If this is a new installation where is your Aperture library located? Internal or external disk? If it is external make sure the disk is formatted as OS X Extended.
In either case post back with the specifics of your system.