Problem with Morph targets and Normals

Hello everybody.

I’m in need of help in order to solve a massive problem. I’m working on a customizable AND dismemberable character. I created a dismembered model using blender and altered its normals in order to hide all the wounds. I therefore created a morph target altering the body shape paying attention to not distort the areas containing wounds. This worked perfectly in Blender (see attached pics 1, 2 and 3) and wounds are correctly hidden after the fbx import into unreal engine 4 (see attached pic 4), but they are revealed again after I increase the value of the morph target (see attached pic 5). I’m using Blender 2.76b and Unreal engine 4.9.2. Am I doing something wrong during the export and import process?

If you have any suggestion or any other further question, please feel free to ask. I’m completely stuck at this point and can’t go any further in the project.
Thank you in advance!!!