There is a known issue in this scenario. The RadWindow moves its content in the DOM (so as to render it as a direct child of the form element) and this breaks the RadEditor. There is a simple workaround, however - call the Editor's onParentNodeChanged() method when you show the RadWindow:
. . . >
. . . . . .
The exact behavior you describe, however, is a result of the display: none being set to the RadEditor's parent:
"padding: 5px; display: none;"
<telerik:RadEditor runat="server" ID="RadEditor1"
Once removed things should be working as expected.
the Telerik team
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