If I understand the scenario correctly, you have an <asp:Panel> inside the left RadPane and you are adding an image to it in the OnLoad
event of this pane. I tried to reproduce the issue with such a scenario, but to no avail.
Regarding to the update panels you are using - does the issue could be reproduced even if you remove them from the page?
You do not mention which elements are being updated with the update panels. Please, note that there are some specific things in updating a RadSplitter - you could find more information in here
If this is not the issue - could you, please, prepare a sample fully runnable project reproducing the issue so we could examine and debug it locally?
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