The Windows port has (for some time now) been improperly constructing its WindowCloseTimer objects. Ever since Bug 53733, ActiveDOMObjects have been required to call suspendIfNeeded so that DOM objects are in their proper state during script execution.
<rdar://problem/19399740>
Created attachment 244161 [details] Patch
Committed r178041: <http://trac.webkit.org/changeset/178041>