kern/49847: tar xzf /zfs/foo.tgz fails reading from zfs but succeeds in pipeline

[riz%NetBSD.org@localhost]

>Number:         49847
>Category:       kern
>Synopsis:       tar xzf /zfs/foo.tgz fails reading from zfs but succeeds in pipeline
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Apr 20 20:25:02 +0000 2015
>Originator:     Jeff Rizzo
>Release:        7.99.9
>Organization:
>Environment:
NetBSD zfs1.lan 7.99.9 NetBSD 7.99.9 (GENERIC) #7: Fri Apr 10 15:52:57 PDT 2015  riz%cassava.tastylime.net@localhost:/scratch/amd64/obj/sys/arch/amd64/compile/GENERIC amd64

>Description:
When the path /zfs/test1 is a ZFS:

zfs1$ mkdir /tmp/foo && cd /tmp/foo
zfs1$ tar xzf /zfs/test1/games.tgz
gzip: data stream error
tar: End of archive volume 1 reached
tar: Sorry, unable to determine archive format.
zfs1$ gzip -dc /zfs/test1/games.tgz | tar xf -
zfs1$ ls
etc usr var
zfs1$

No idea why one fails but not the other.
>How-To-Repeat:
create a zfs and put a .tgz file on it
try to extract the .tgz file with "tar xzf /path/to/file.tgz"

>Fix:
none given