When the extra parameter is used in jQuery.event.trigger and there is no default event for the type and the element does not have "handle" data, the event fails in Opera.

The problem occurs because val is undefined when this line is executed:

var ret = extra.apply( elem, data.concat( val ) );

This change fixes the problem:

var ret = extra.apply( elem, data.concat( val || false ) );

I'm not too familiar with the internal event code, so I'm not sure if that is an appropriate default value. I tried using null, but that causes the error as well.

I came across this problem using the Droppable plugin with a callback (drop, over and out all cause the problem).