SPARTAN-OPS dead corpses disappear very fast

in SPARTAN-OPS when you play alone like the single-player campaign, dead covenants corpses disappear very very fast in front of you, the dead corpses only stay 3–5 seconds and then they disappear

but in the campaign you can kill 20 covenants and their dead bodies stay and dont disappear until you go far faraway to other area

a think they must fix this and put the same campaign-skulls in spartan ops