I've had this happen before, too. I admit that I don't measure the M&P carefully. I just made up my own "recipes" for it. But yes, the oils can rise to the top. I find that if I beat the ever loving snot out of it with a whisk, you can incorporate it better and it won't have that sludge on the top.
You can just melt it back down and whisk it. It'll change the color some, depending on what you put in it, but it will still work great.
i'm not really familiar with mp additives, but afaik the rule of thumb is 1T of additives ppo (per pound of oils). 1.5 cups is roughly 350 grams, def less than a pound. just maybe that is the reason for it? what kind of base are you using?
Actually I think it is the exact opposite. The oils rose to the top of the soap. I had to soak up the oil with a napkin. It appeared that all of the olive oil had risen to the top. It was weird. I'm thinking that I put to much oil in.