Last night I started an unprivileged bulk build, and all packages except 
the first failed. The cause for it was that the WRKOBJDIR had been 
created in /tmp and inherited the group owner "wheel", which isn't part 
of my bulk user's groups. The inheritance went further, so all files in 
WRKSRC had that group, too. Then pax(1) -rw -pe tried to copy these 
files into PREFIX, which failed because the group could not be set.

It took me quite a time to find the cause, so I want to save you the 
time of bug-hunting similar issues.

Roland