Category-based feed still contains non-category episodes

Hi all!

I just tried to establish an “English episodes only” feed by using the Category-based feeds. After enabling the categories for episodes in the publisher settings and assigning the relevant episodes to the category, the resulting feed does still contain German episodes (which are not in the category) in some podcatchers (such as Overcast or Apple’s Podcast). If I have a look at the XML feed, the German episodes are not included.

Here are Screenshots from the XML-Feed in the browser (that contains only English episodes and the same feed subscribed in Apple’s Podcast App:

What am I missing? Can anybody give me a clue?