Energetic protons (0.5--20 MeV) appear to be trapped between a pair of shocks associated with the major solar flares of April 15 and April 28, 1978. Prolonged trapping (for a period of weeks) is implied by the large count rate enhancement and the large range of radial distances and longitudinal angles over which the trapping is observed. Shocks associated with both flares are detectable in the Pioneer 10 and Pioneer 11 plasma analyzer data. These shock/flare associations are different from those previously published by others studying the interplanetary events. The evidence for trapping has not been recognized heretofore most likely because of the unobservability of the April 15, flare (located ~150¿E of the sun-earth line) and of the faintness of the signature in the plasma data of one shock in each pair. The apparent ability of a shock whose plasma signature is extremely weak to confine MeV protons in the outer solar system may have significant implications for cosmic ray studies. Contrary to earlier analyses of these data, the results of our analyses also imply significant azimuthal asymmetry in plasma and energetic particle behavior even at distances as far as 16 AU from the sun. The combination of these observations provides evidence for unexpectedly complex interactions in the outer solar system between energetic particles and solar wind plasma.