Creating a jail in a very recent CURRENT r342378 and ports latest with:
# poudriere jail -c -j freebsd-r342378 -m svn+http -v head@r342378
works fine but let stay the created tree below
I don't know if the tree could simple be removed after creating the jail. In any case, this tree gets in the way if you want to transfer /usr/[src|obj] to some other host for an installation there.