I'm using the merge path tool to combine some closed shapes in Illustrator for a very curvy and precise logo. The merge is working for most of the logo, but for certain shapes it is not. I've tried bringing different shapes to the front and back, but some shapes do not seem to to be effected. The merge leaves both paths there and if I try to -pen the unnecessary paths away, that part of the shape deletes out. How do I get this to work consistently?