After looking at your file in v21, there seems to be no issues at all. I do not have v18 loaded any more. My question to you is this. The drawing you uploaded, is it supposed to represent the "ivory" inlay, or the pocket which the inlay will sit in the cue?
If it is the inlay, you would cut it out of your stock using "Path milling, if it is in the but it would be a pocket. Now they have to be different sizes, so the inlay, with the glue, will fit into the pocket.