An energetic particle dispersion feature observed by the ISEE 1 medium energy particle instrument is identified as an old phenomenon, injection of hot plasma followed by drift dispersion, seen from a new viewpoint, the highly elliptical ISEE orbit. The feature is characterized by enhancements in the electron and ion fluxes in the energy range 20 keV to 200 keV and is seen between 5 RE and 13 RE. Events with this signature show strong energy dispersion, with the highest energy ions and electrons arriving first. The feature is not always present for both ions and electrons or at both 30¿ and 90¿ pitch angles. The species and pitch angle of particle in which it is most likely to occur vary with local time. Because the signature is seen on both outbound and inbound satellite passes, always with high-energy particles arriving first, it cannot be due to satellite passage through stationary spatial structures set up by steady state convection. Creation of the events can be qualitatively explained by using an injection boundary model with a magnetopause that functions as a particle absorber. Such an absorber is necessary to explain the predominance of electron features and scarcity of 90¿ ion features in the morning and the predominance of ion features in the afternoon. Signatures seen by satellites with highly elliptical orbits are often interpreted as effects of satellite motion through spatial boundaries. Here, it is shown that the intrinsically time-dependent injection boundary model can qualitatively explain the features that we see in data from a satellite that makes an almost radial cut through the magnetosphere.