When changing the “Is Active” value on a category for a particular store view the “Use Default Value” checkbox always shows as checked after the category changes are saved. Upshot is that all categories are either active or inactive for every store view because they’re all set to use the default value.
To reproduce: Uncheck “Use Default Value” and make a change to the “Is Active” value and save changes. When the page redraws the “Use Default Value” checkbox will be checked and the default value will have been changed.
I see the same behaviour in the demo store (http://www.demo-admin.magentocommerce.com). Incidentally, when changing “Display Mode”, for example, it works as expected - the “Use Default Value” checkbox stays unchecked!