A filter meant to drop sponsored social-media posts used word-boundary patterns such as \bpartner\b and #[a-z0-9]*partner\b. Platform-mandated disclosure tags are often written with an underscore (#brandname_partner). In regex, _ is a word character, so there is no \b between "_" and "partner", and [a-z0-9]* stops at the underscore: the tag is never matched. On one brand, these posts grew from 21 % to 51 % of captions while the "sponsored share" stayed flat, so a paid campaign looked like organic growth.