Why are more recommendations added to my manual bundles?

By default, your manual bundles are completed with other types of recommendations (up to reach the maximum number of recommendations configured in the 'Recommendation Tuning' section):

If you don't want more recommendations added to your manual bundles, i.e., if you want your manual bundles to display exactly as you configure them, you can do it easily with the option 'Exclusive manual bundles':

You will find that option under the 'Recommendation Tuning' section in the app preferences page.