Killing a major or above with a primary solar weapon and with a full solar super will grant the solar surge x4 buff one time. Once the buff expires it will lock me out of gaining the buff upon killing another enemy until I die. This does not occur on any other subclass only on solar. I've tested this in the firing range and replicated it multiple times. I've tested this with different solar weapons (adhortative, nullify, sleeper stimulant, and cataclysmic)