What's Going on with this Cupped Floor?

Craig DeWitt Headshot

Here's a question related to my fellow blogger Howard Brickman's last post about what causes cupping:

Situation: The wood flooring is cupped with spots that have raised off the slab. The construction from the bottom up is slab, 6-mil poly, two layers of 1/2" plywood stapled together and floating on slab, 15# red rosin paper, 5 & 6" solid red oak stapled to the floating plywood. The slab was 85% RH, the plywood was 14% MC, and the oak was 8% MC. The poly was full of holes from protruding staples.

So, what is happening?

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