6.5 auto_install fails due to custom /var/tmp?

While trying to PXE install a 6.5 machine I was hit with this failure:

Installing bsd 100% |**************************| 15163 KB 00:00
Installing bsd.mp 100% |**************************| 15248 KB 00:00
Installing bsd.rd 100% |**************************| 9984 KB 00:00
Installing base65.tgz 99% |************************* | 189 MB 00:00 ETAtar: Unable to remove directory ./var/tmp: Device busy
Installing base65.tgz 100% |**************************| 190 MB 00:14
Installation of base65.tgz failed. Continue anyway? [no] no

which I suspect is related to this:

/ 1G
swap 4G-16G 10%
/tmp 2G
/usr 4G
/usr/local 2-6G 10%
/var 10-20G 20%
/var/tmp 10-20G 15%
/var/log 20-40G 30%
/u 1G-*

I've never run into this until today, when I tried to carve out an explicit
/var/tmp. Autopartitioning be able to handle /var/tmp, no?

--lyndon