This happens after r190717 when you open a popup menu and without selecting any option it's dismissed (press ESC or click somewhere else). This is because I removed the code to track when the menu is unmapped, thinking that it was no longer necessary. But we need to send the DidChangeSelectedIndexForActivePopupMenu to the WebProcess with -1 as index to keep the web process in sync.
Created attachment 268693 [details] Patch
Committed r194886: <http://trac.webkit.org/changeset/194886>