I am seeing this exact issue in my project as well. I started right after v33.0.
Initializing a material including parameters via a class variable initializer produced a material that could not be set:
var my_material : MaterialHere_material = MaterialHere_material{}
I could call .SetMaterial() using my_material, but the new material would not be applied.
After I moved my material initialization inside a method on the class, the issue was fixed and the material could be applied and parameters changed.