Jquery UI Selectable - event fires twice when browser was left

I have a selectable table with jquery ui and metakey active. For testing purpose i am alerting whenever a row is selected or deselected. This works as long as the focus remains within the browser (tested with Chrome, latest release). But when i click on an other application window and then return to the table directly clicking on a row, the selected event fires twice (two alerts).

$("#sel-table tbody").bind("mousedown", function(e) {

e.metaKey = true;

}).selectable({

selected: function( e, ui ) {

alert('Selected')

}

},{

unselected: function( e, ui ) {

alert('Unselected')

}

}

);

Complete code on JS Fiddle (https://jsfiddle.net/tmoeller/pg9264d1)

Is it a bug or feature. If feature, how can this be avoided?? Any ideas on this??

tmoe