For anyone interested, the answer turned out to be to hook into the DataContextChanged event of the targeted UI element (button1.DataContextChanged in this case).

I found it, it's AttachedPropertyBrowsableForChildren: http://msdn.microsoft.com/en-us/library/system.windows.attachedpropertybrowsableforchildrenattribute.aspx[^] Will be nice to have that working now!