Test case: http://persistent.info/webkit/test-cases/counter-reset.html
The test case simulates a normal <ol> via an <ul> that uses CSS counters and generated content. Press the 'Deintent "Four"' button. The "Four" list item is unindented, which gives it a list counter of 2 (correct). Then the items that follow it should restart the second-level counter, and thus have counters of "a", "b" and "c" Instead they end up with "c", "d" and "e", continuing the count from the "Two" and "Three" items.
To prove that this is an invalidation issue, the entire list DOM hierarchy is cloned and appended to the document. The clone renders correctly (Gecko renders the test case correctly).