This topic reminds me of the old, endless diatribes that go something like this:
"The SUX-2000 camera has banding/hot pixels/etc. when I take an hour-long exposure at ISO 128,000 of a bat in a belfry! Banding! Can you believe it? The SUX-2000 is junk! I'm not going to buy one, and neither should anyone else! I'm going to make 100 posts on 10 forums so no one else buys it either!"
People, every product has limitations and corners of operation where caution is required. Very long exposures in bright light, quite possibly facing towards the sun, while wearing nearly-opaque 12-stop ND filters is by almost any account an unusual and, in my opinion, extreme condition.
It's not like flare of one sort or another (if it's that, and if it's the lens and not the stacked rings, etc.) is a totally unknown problem or unacceptable flaw that results in the utter rejection of a lens either. Most people accept that flare happens from time to time. If the effect is real and repeatable and proven to be the lens, the answer may very well be "in those 1 out of 10,000 tasks, use a less complex lens like a 50mm."
It is not reasonable to expect any product, at any price, to be absolutely perfect in every way, no matter how extreme the test. A problem such as this, if real, does not make the lens fatally flawed any more than any other product that doesn't turn you into the next Ansel Adams or cure "manhood problems" during use, etc.
I have this lens, and it's magnificent. If you reject yours as unacceptably flawed, well, good luck finding an acceptable spouse...