Selection feather breaks after a certain point

[HungryDoodles]

So, I was having fun with sky colors, had to vary colors, outlined approximate area and opened "refine edge" for selection.
Selection features: touches edge, has at least two corners, performed on a 4096x4096 canvas.
Feather value - result:
Below 84.7 - works fine.
84.7, 84.8, 84.9 - no selection (blank black preview).
85 and above - absolute haywire (see attachment).
Not sure if it's true, but looks like (MAYBE) convolution (or similar blurring method, fast blur for exapmle) ran out of working space. Preview shows truth, if I click OK, it will really use this noisy selection.

Haywire feather.jpg (588.72KiB)Viewed 526 times

P.S. I really wonder how could this happen... I love digital noise.

[support]

got it