Dynamic types are used whether the option is checked or not.
Break at the line with the comment - both objects are displayed as Derived.
Now step to the next line - both objects are displayed as Base.
This is the expected behavior when "Use Dynamic Type" is checked, but when it is unchecked - b should always be Base and d should always be Derived. That part is broken.
This happened long ago, reported as
QTCREATORBUG-7504, and I fixed it. Now it happens again (I can't tell for sure on which version the regression was introduced).