Scriptaculous "blinddown" not seeing the height of updated content of div

I currently have a div called “updateDiv1” nested within a bigger div called “htf”.

When someone loads the page initially, “htf” has “display:none” as its style property. There is one line in the “updateDiv1” div, which cannot be seen because of “htf”'s diplay property.

I have placed my code below; basically, when the send function is activated, I want “updateDiv1” to show the new content, and “htf” to load it with the slidedown animation. It works the way I want it with one exception: The BlindDown animation animates to the bottom of the “old content” height (1 line) regardless of how large the newly updated content is, and then “jumps down” to the bottom of the new content after the animation is loaded.

My question is, how can I get SlideDown to recognize that the updateDiv1’s content has been changed, and to animate to the bottom of the new content instead of the old content?

Here is my current function:

function send(tval){
var params = Form.serialize($('commentsForm'+tval));
new Ajax.Updater('updateDiv'+tval, 'ajax.php', {asynchronous:true, parameters:params});

function tester2(){
new Effect.BlindDown('htf');