There is a Dispatcher call without checking in the dispatcher call for NULL. This lead to NullReferenceException in huge production code. Available in R3 2016 SP
The issue can be reproduced with DatePicker inside of ComboBoxItem ItemTemplate. Available in LIB Version 2016.3.1010, it will be also available in the 2016 R3 SP1.
The issue is not reproducible since R2 2016 SP1 version.
DropDownButton is leaking.
Property values are inherited from the logical parent and not visual parent (as in SL). Thus ContentPresenter and ContentControls children doesn't get the new Foreground property. This can not be workarounded with VisualStates, but Triggers only Reason for declination: WPF limitation