Hi Jean-Pierre,
Thank you for the provided information.
Actually the fix for this item is already implemented and it will be available with the next Latest Internal Build. You will be able to download it from your telerik account later today (version 2019.3.1125). Please, give it a try and let us know how it goes.
Regards,
Vladimir Stoyanov
Progress Telerik
I also tried to change the UpdateSourceTrigger to PropertyChanged and it was working fine. On the other hand, when using "LostFocus", the ValidationRule and CanExecuteOkCommand gets invoked before the exception is raised (just to let you know).
Thank you