In that case the framework validation should be raised as a string value cannot be assigned to a numeric property. The Binding of a PropertyDefinition will take care of this framework validation and such an error message will be shown out of the box.
In this case, the setter of the property will not be invoked at all. You can also test entering a string value for a numeric field on our WPF Demos with RadPropertyGrid.
If this is not your case, would you please extend my demo project or create a new one to better illustrate your question and send it to me?
You can open a new support thread and attach the sample there.
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