I dont think it should happen, and I cant say I remember it happening to me, but if worse come to worse you can try eliminating the extra bits by enclosing them in a primitive object and doing a bollean subtract, or enclosing the bit you want to keep in a primitive object and doing a boolean intersection.

"I paint that which comes from the imagination or from dreams, or from an unconscious drive. I photograph the things that I do not wish to paint, the things which already have an existence."
Man Ray, modernist painter
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