Bug in jQuery animate

Calling animate with empty hash prevents that element from animating
again
$("#piece_1").animate({top:200}) => moves
$("#piece_1").animate({}) => nothing happens (as expected)
$("#piece_1").animate({top:100}) => no longer moves
This is on jQuery 1.4 (and also 1.3)
From looking at the source, it seems that the animation never stops
(i.e. it's queue still has 'inprogess')
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