Mesh unwraps in undesired way (seams are not obeyed) 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.

Here is link to blend file:
https://www.wetransfer.com/downloads/db48ae49a47dd31103bb5bdd1c233aaa20160405141634/d98e72b1b5847bc4dde682751860aaba20160405141634/a98a07
Your mesh has some problems.  You have not joined the wing to the body correctly which has left unconnected edges and interior faces. This is the cause of the extra UV islands.

You can see the problem area by clicking Select -> Select All By Trait -> Non-manifold.  You should remove the interior faces and connect the wing to body for the mesh to unwrap properly.

You also have several nasty poles that may affect the way the mesh deforms once rigged.  If you are intending to fix these, it might be worth altering the topology before you UV the mesh.