I am afraid, I had now success in reproducing the problem. I put a RadTabControl with 3 RadTabItems -- one for a TextBlock, one for a RadChart and one for a RadGridView and loaded this window on a button click (as per your description -- it should not be the first window loaded). Still, everything works a expected. You can get this sample and start to apply any custom styles and/or themes you use to see which change will trigger the problem. Once reproduced, please send it back to us for investigation.
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