I have lens casts with every lens, and its the same for every lens, on both my own P45+, and my loaner P45+ (while the one i own is in denmark.)
It appears identically across both P45+'s, and in both C1 3.7.7, and 3.7.8 beta. In lightroom or ACR its more apparent with a slight "centrefold" issue on top.
This is obviously not lens cast, but can be fixed with the LCC tool. It should not be like this, and as you write on your blog, it appears exactly the same way you describe it, greenish tint to the left side, and magenta to the right.
I'll post back when I hear P1's explanation for the "cast". You should seriously consider opening a support case with P1.
-axel