You can fix simply this by yourself. It's too easy. 
What you needed it's just read this below:

Open needed file in this path: 

Scripts\Materials\mat_canvas.lua

Find the setting there:

piercing_resistence = 0
___________________________
If it is 0, then this material is shot through, and enemies can see through it
If it is equal to 7, then this material is shot through, and enemies cannot see through it
If it is equal to 15, then the material is not shot through and the enemies cannot see through it