We report an anomalous dispersion of charged excitons in photoluminescence experiments on a two-dimensional electron gas subjected to a quantizing magnetic field around v=1/3. We have found that the anomaly exists only at a very low temperature (0.1 K) and an intermediate electron density (0.9×1011 cm−2). It is explained to occur due to the perturbation of the incompressible liquid at v=1/3. The perturbation is induced by the close proximity of a localized charged exciton which creates a fractionally charged quasihole in the liquid. The intriguing experimentally observed puzzle that the anomaly can be destroyed by applying a small thermal energy of not, vert, similar0.2 meV is thereby resolved, as this energy is enough to close the quasihole energy gap. This work presents a probe of the quasihole gap in a quantum Hall system.