I was rebuilding the example I had been sharing on V6 probably for the first time.
In the attached file I have two polysrfs. The one in gray behaves bizarrely. The polysurface in read passes clear through yet it will not subtract or split. In fact, if I draw a line along the top edge of the red, I cannot use it to trim gray.
If I intersect the curve at the top is open for no apparent reason.
I can trim slightly above the top of red or slightly below but not where I need it to cut.
I am curious what is going on here now.Problem Subtract.3dm (3.5 MB)