you converted to Instancer? (as on your screenshot)
if so, why don’t you convert directly to Particle System? it is the next option and it will do all for you
here is my test (as i see you are using 0.9.x version, so this last from repo)
emitter
sphere
try from scratch, use to direct to particle system option like on screenshot below, from your description i have no idea what you have wrong, i am sorry… if it doesn’t work, i would need blend and ply to have a look…
image is generated and it is not stored anywhere, it will stay in blend as long as it is used somewhere. you delete the objects where it is used, eventually will disappear. that is why it is referenced in emitter object material even though not used for anything
and to prove it is particle system, here is some explosion 
