While implementing the fix for https://bugs.webkit.org/show_bug.cgi?id=19111 I noticed this. Setting `sessionStorage.getItem = "someValue";` should fail, for example, even though it's perfectly valid to do `sessionStorage.setItem("getItem", "someValue");` I'm going to fix this after 19111, and the layout test I have that demonstrates this will be attached shortly.
Created attachment 21222 [details] layout-test-style example that shows the problem for all properties
FYI I asked a very similar question on WhatWG (coincidentally) recently: http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-May/019915.html