As part of http://trac.webkit.org/changeset/40005, setUsesBeforeAfterRules was added as part of the element construction instead of as part of the insertion for 2 elements. Moving such an element from a document to another could lead to the before/after rules not been enabled on the new document.
Created attachment 27590 [details] Proposed change: move toggle into insertedIntoDocument
Comment on attachment 27590 [details] Proposed change: move toggle into insertedIntoDocument r=me
Landed in r40921.