Now that I have had my car a few weeks I am just returning to other threads to tell people I have the same issues
My G61 wiper does the exact same thing. I noticed it over the weekend getting the dog out of the boot and my rear screen now has a coat of winter grime on it.
This post immediately popped into my head and now I can't unsee it. I have now watched the wiper in my rear mirror and can see it doesn't go the full 180 degrees......
ETA: I am RHD