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I believe it depends on the application and how they have it setup. But I'm fairly certain that dtube takes 25% from both the author and curation rewards. So it's a total of all rewards on a post. But again, you might want to check with each application to see.

Wow thats really something that should be disclosed in a person's post to let the upvoters know.

I agree. It should be posted somewhere so everybody knows.