This is almost certainly due to a difference between the GTK+ EventSender implementation and those for other platforms.
Created attachment 58092 [details] Fix for this regression
Comment on attachment 58092 [details] Fix for this regression So drag mode is the "official" way of disabling the queuing of events?
In the case where an event is queued only because the mouse button is down, dragMode is the "official" way to disable queueing of events.
I still don't understand dragMode. I can't remember if ap or anttik added it.
FWIW, Darin Adler added dragMode. I added event queuing.
Comment on attachment 58092 [details] Fix for this regression My understanding reading Mac's event sending controller matches yours. What could possibly go wrong, anyway? Right? Right?
Comment on attachment 58092 [details] Fix for this regression Clearing flags on attachment: 58092 Committed r61291: <http://trac.webkit.org/changeset/61291>
All reviewed patches have been landed. Closing bug.