Problem with portupgrade - "could not find a temporary directory"

[Kent Kuriyama]

This problem is self-inflicted but I can't figure out what I did to cause
it.  When using 'portupgrade' to upgrade software I get the following
message:

root at monitor4:~ # portupgrade -fp dri
[Reading data from pkg(8) ... - 635 packages found - done]
** Listing the failed packages (-:ignored / *:skipped / !:failed)
        ! graphics/dri (dri-9.1.7_6,2)  (could not find a temporary
directory)

The environment variables are set:

PKG_TMPDIR=/tmp
TMPDIR=/tmp

I am unable to find the string "could not find a temporary directory" in
the source tree of portupgrade.  Does anyone know what could cause this
message?  Thanks.

Kent