The sticky polymatroid conjecture

Let $h$ be a polymatroid, and call it sticky if any two extensions of $h$ have an amalgam. A polymatroid is modular when its rank function satisfies the modularity condition for every pair of subsets.

Sticky polymatroid conjecture. Every sticky polymatroid is modular.

The statement extends the sticky matroid conjecture from matroids to polymatroids. The source gives no resolution or evidence establishing its status.