cat_is_ancestor_of does not work anymore

Hi,

I use is_category( 2 ) || cat_is_ancestor_of( 2, get_query_var( ‘cat’ ) ) as Widget logic in the Category Sidebar for 1 year. It worked perfectly before. Now it doesn′t do that anymore (since quite some time).
It only works, if the parent category (2) is set.

Did something change resp. break?

Best regards and thank you in advance.
Markus