Thank you for the provided video.
I tested the described scenario in a sample project on my end, however I was not able to reproduce the observed on your end behavior. That is why I am attaching the sample project I used for testing purposes. May I ask you to check it out and see how it differs from the setup on your end? Are the custom UserControls necessary for the issue to be reproduced?
If you find it possible, can you modify the sample project in order to replicate the design time exception and send it back in a new support ticket (since projects cannot be attached to forum posts)? This way I will be able to investigate the scenario and better assist you.
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