The effect of electrostatic dipole interactions on the wetting behavior of two-dimensional droplets, approximated by circular segment shapes with contact angle a, is investigated. a depends on the geometric structure far away from the three-phase contact point. We theoretically find metastable a-values associated with transitions from complete wetting to partial dewetting, triggered by minute changes of the film area, the surface potential of the coexisting phases, or their line tensions. The predictions are confirmed experimentally in a Langmuir monolayer model system. The wetting instability may influence intramembrane biochemical reactions between protein species dissolved in coexisting phases via the length of the contact line between the phases, the only region where chemical reactions between the species are possible.