Thank you, RB Strautman!!!
This worked like a charm. I only had to open the movie card twice. The first time, I removed all additional genres and set the main genre to "Not Defined" and clicked "OK". The second time, I set the main genre to "Dark Comedy", then filled in all the additional genres, and clicked "OK".
I have saved this correspondence in a text file and will keep it in the archive with my installation files and license. It is valuable information that will not get lost.