The loaded into the ImageEditor image is not downloaded with its original extension if a query string is added to the end of the image name. It is saved as PNG instead:
Steps to reproduce:
1. Run the code below and open the SaveImage dialog
2. Chose the "Download image" option and click OK
Result: The image is downloaded as PNG
<telerik:RadImageEditor RenderMode="Lightweight" ID="RadImageEditor1" runat="server"
ImageUrl="~/images_1/test.jpg?test123" Width="100%" Skin="Silk">