That one is cross firing. Mine (.410) did, too, when first tested with 1/2 oz. loads. At a suggestion, from you if I'm not mistaken, I tried the WW 3/4 oz. factory loads. They regulated it perfectly. That suited me to a "T" because it is a hunting gun and I wanted to use the maximum loads in it, it being a .410.
I'll betcha' a heavier, slower load would do the same in the test gun in that article. Slower loads allows the payload to remain in the barrel a tiny bit longer, and the heavier load creates a bit more recoil, both of which helps in bringing the pattern back towards POA, when it is crossfiring.