I made the same experience that the Windows ACL setup in the ZFS Volume/Dataset GUI does not work properly. It seems to default to a specific, unusable permission, independen on what you select in the GUI:
owner@:rwxp--aARWcCos:------:allow
group@:r-x---a-R-c--s:------:allow
everyone@:------a-R-c--s:------:allow
br
owner@:rwxp--aARWcCos:------:allow
group@:r-x---a-R-c--s:------:allow
everyone@:------a-R-c--s:------:allow
br
