Still, I am not able to replicate the issue with the provided code. Can you confirm that you're using our latest release? Is it possible to try create a runnable sample and send it to us, so we to be able to research the case? Note that you should open a support ticket and attach the sample there.
I would like to make a note here - I've noticed that you've merged the theme resource dictionaries inside the UserControl - the recommended approach is to merge them in App.xaml, as for example, EdtiAppointmentDialog, when shown, is placed in a different visual tree and in the current way, will not receive its Style.
I am looking forward to your reply.
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