Effects won't animate if there's a > selector

With this code:

#contact > .myDiv {
	height: 478px;
}

<div id="contact">
  <div class="myDiv">
  </div>
</div>


var mydiv = ...
mydiv.show('blind', 'slow', function() {....

mydiv is shown, but not animated.

If I change to code to:

#contact > .myDiv {
	
}

<div id="contact">
  <div class="myDiv" style="height: 478px;">
  </div>
</div>


var mydiv = ...
mydiv.show('blind', 'slow', function() {....

It animates correctly. This seems to be reproducible every time that the attributes that need to be modified for animating is defined in a CSS selector with a ">". (and it's not limited to blind).