This is fixed with a (clean) cherry-pick of upstream commit 3b0ba3ba99b8a3af0fb532bf264629436b1abd84 [1]. Note sure in which format patches are desired for pkg-zfsonlinux..
A local test build including the above commit works as expected.. 1: https://github.com/zfsonlinux/zfs/commit/3b0ba3ba99b8a3af0fb532bf264629436b1abd84
