If Paragraph has applied style, and this style has associated list, and the paragraph is removed from the list locally, then on import the paragraph is added to the list.

The additional numbering could be removed from the paragraph by changing its style:

foreach (var p in this.document.EnumerateChildrenOfType<Paragraph>())
{
    if (p.ListLevel == 0)
    {
        var style = new Telerik.Windows.Documents.Flow.Model.Styles.Style("NoListStyle", StyleType.Paragraph);
        style.ParagraphProperties.CopyPropertiesFrom(this.document.StyleRepository.GetStyle(p.StyleId).ParagraphProperties);
        style.ParagraphProperties.ListId.LocalValue = null;
        style.ParagraphProperties.ListLevel.LocalValue = null;
        p.StyleId = "NoListStyle";
    }
}