Hello!
Thanks for this suggestion, the probem has been solved after I binded ContentTemplate the Tag property with a DataTemplate. A icon was shown in both locations normally.
However, the same approach did not work, when I used a custom attached property instead of the Tag. When a datatemplate is assigned to the attached property, an icon is always shown on the button but does not appears in the QAT. So, it is a reverse error. As I may guess, attached properties are not cloned for QAT
Anyway, I am fine with using the Tag property.
Cheers, Ilia