I ran into this as well.  First of all, and you may already know this, if you are using an updatepanel to show the Editor make sure the updatepanel is inside the div that you are using to define the dialog.  Also, on the open event for the dialog make sure that you move the div's parent inside the .net form tag. You have to do these two things because the jQuery dialog control creates the structure for the dialog as the last object in the body tag and then moves the div that you want to use inside of it.  This moves the div out of the form and any updatepanel that it might be in.

 

   After that, to solve the problem that you mentioned, I had to disable the dialog's show animation to make the editor work.  I did this only for Safari (our app doesn't support Chrome). 

 

Hope this helps,

bczengel