Exclude an app in Clipboard history?

I've looked in the preferences and found an option to add an app so it should be excluded by the clipboard but it doesn't seem to work. I've added the app InDesign CC2019 in the list, but every time I copy something from that app, it's listed in the clipboard History. Since I copy texte from one document to another all day long, it's getting ridiculous and it seems to slow down my computer considerably. If I quit KM, everything is fine so I think KM involved in the slow down somehow. I couldn't find more info on this. So how does the exclude list actually work?

The Exclude list works for me, but it's also a good idea to set the limit of the number of clipboard entries saved. That can speed it up considerably.