This paper proposes a novel account of a derivationally opaque aspect of ATR harmony in Eastern Andalusian. Harmony in the language is driven by Positional Licensing: [-ATR] originating on final vowels must spread to the stressed vowel. Intervening post-tonic vowels optionally also harmonize, as do pretonic vowels. Typically in licensing-driven systems, if harmony is unable to reach the licensor, harmony does not affect non-licensing positions either. Not so in Eastern Andalusian: high vowels do not harmonize, but a stressed high vowel does not prevent unstressed vowels from harmonizing as normal – harmony can overapply on these vowels. The analysis, couched in serial Harmonic Grammar, develops a new mechanism called persistence that accounts for this opacity. Under persistence, once a feature satisfies Positional Licensing by spreading to the licensing position, Positional Licensing remains satisfied for the rest of the derivation, even if the feature vacates the licensing position. This allows a stressed high vowel to harmonize, thereby permitting unstressed vowels to harmonize, too, and then harmony can retract off the high vowel without running afoul of Positional Licensing.