If you copy one of the preset Score Styles in Logic Pro or Logic Express and then try to add a voice to an existing stave by choosing New > Insert Voice, Logic creates a new stave for the voice instead of adding the voice to an existing one.
When you open a Score Style in the edit window, the insert mark's default location appears above the first existing voice, as shown below.
When you insert a new voice, it gets placed at the position indicated by the insert mark. In the case of a Score Style, this would be before the first voice. Because a voice cannot exist without a stave, Logic creates a new stave for the voice, as shown below.
To workaround this issue, before inserting a new voice, grab the insert marker in the edit window and drag it down so that it appears below the existing voice, like this:
Now when you choose New > Insert Voice in the Score Style window, the voice will be added to the existing stave.
