Okay, I had a closer look
Input (on my rasbperry)
i2cset -y 1 0x46 0x1 0x50
Thats a value of 80
What it should be
01010000
What it is
0111000
i2cset -y 1 0x46 0x1 0x1 (1)
What it should be
0001
What it is
1000100
i2cset -y 1 0x46 0x1 0xFF (255)
What it should be
1111111
What it is
1111111
Maybe I should try to do it all by myself without the library, but I guess this will take a while since I have no Idea how to operate the shift registers manually.