I determined what was the issued and will post my solution here in case others encounter the same problem.
I incorrectly assumed the .load() call was a synchronous (blocking) call, which it is not. Therefore, the SimpleModal call was processing the empty div before the content had finished being served. I updated the code to use a callback function to display the modal dialog and everything now works correctly: $("#dialog").load("/snippet.html", {}, function() { $("#dialog").modal({ overlay:80, overlayCss: {backgroundColor:"#000"} }); });