I presume the 'issue' to which you're referring is the uneven polatization of the sky? That's what happens when you put a polarizer on an ultrawide lens. The angle of the sun relative to your image plane determines the amount of polarization, and thus the angle of polarization varies continuously with the angle from the sun. So, with a lens wider than about 28mm (on FF) the sky will be unevenly polarized (and as you see in your shot, that unevenness due to the wide FoV also applies to reducing reflections). You can use the effect creatively, or skip the polarizer for those shots if it bothers you.
Side note: I just mentioned – literally, a few minutes ago – the issue I see in your example in the
thread on Lee filters for the 11-24L.
BTW, Promaster filters aren't the greatest. Personally, I'd go with a B+W Käsemann CPL or a high-end Hoya CPL for use with a very sharp lens like the 16-35/4L IS. Promaster filters are cheaper than you might think at least in terms of production cost, they are so prevalent in retail camera shops because they get marked up by a substantial amount, meaning good profit for the store.