Quad with fade shader material is rendered below while physically above another

Hello there,

I have two quads, one above the other. Both are using a material with a standard fade shader. My problem is that quad A is above quad B, but, depending on the angle of the camera, is rendered like it is below ! Here is an image of what I get, depending on the angle of the camera (quad A is a plate, quad B is the black disc):


Why do I get that, and do you have any idea how to fix this?
Thanks!

 

I found this, maybe it answers to my question (if anyone can confim) : https://answers.unity.com/questions/609021/how-to-fix-transparent-rendering-problem.html