I have bird model with symmetric wings on its left and right side. Wings are cutted by the seams from the rest of the body. One wing unwraps correctly, following the seam but second doens't. No matter if there is a seam or not the wing always unwraps as if there was some seam. Even with my symmetric seam it unwraps like there was some extra seam near to my.
I attached the screenshot of unwraped model with selected undesired edge cut.