We are aware of this issue and I have raised its priority in our bug tracking system. You can track its progress here
in our Feedback portal where you could find a resolution. For your convenience, I am pasting the steps to workaround the issue:
1. Follow the Custom Built-in dialogs approach (http://demos.telerik.com/aspnet-ajax/editor/examples/externaldialogspath/defaultcs.aspx
) to use an external and later modified Plain Paste Dialog - the MozillaPasteTextDialog.ascx;
2. Find the clientInit() method trough the client-side logic of the MozillaPasteTextDialog.ascx file;
3. Remove the this._container.focus() line.
I hope this will help you resolve the issue.
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