The dialog's content is loaded through an Ajax request, i.e. it is normal that the first request be a bit slower than the subsequent. The control uses only one dock to show the content of the dialogs and we are aware that the previous content is still visible and this may become confusing. A solution for this issue, perhaps using an AjaxLoadingPanel, will be applied most probably for the service pack.
As far as the AddText functionality is concerned, we will check what are the options to improve upon it and will decide what the best solution there will be.
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the Telerik team
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