Alpha Blended with PBL is darker than expected

If I create two shaders, with default Blinn-Phong. One Opaque (RGB into Diffuse) and one Transparent (RGB into Diffuse, A into Alpha) and leave everything else default both shaders give me equivalent brightness. With the Transparent/Alpha Blended one, anywhere I am using Alpha = 1 it is the same.



If though I change these two shaders to PBL, the Alpha Blended one is darker.