That is because there is an amount of maximum exp. to get from a monster...
If the monster gives yo too much experience, you should get down the multiplier of the code...
Maybe x128 or x256 will be just fine.
@Xdqwerty, to answer your question, they're a fusion Brit-pop/J-pop/electronic band with a woman vocalist. Flamingo is hands down their best known song but they've got a ton of other really good songs