Blender exports one extra triangle

Hello, when I export .obj into my game dev studios engine, it seems like “last” exported triangle doubles. Like on this picture :


Also if I export one plane, it will have also one triangle doubled (bright like on example above).


We managed to get rid of that last doubled triangle by manually removing vertice coordinates from file that our game engine generates from that .obj file.
When we export objects from 3ds max everything is fine, only when we export with blender thing like this one happens.
So if anyone experienced same thing or has an idea about solution it will be really nice.

My export settings are:


Best regards!