lossage with successive builds on netbsd-6 branch

[Christoph Badura <bad%bsd.de@localhost>]

When I do two (or more) build.sh runs in a row switching MACHINE with -m
only the first one runs to completion. E.g.:

./build.sh -j8 -U -O obj -m i386 tools release >& build.i386.log
./build.sh -j8 -U -O obj -m sparc tools release >& build.sparc.log

The same sequence works for netbsd-5.

The value of -O doesn't seem to matter.  Building without -O doesn't make
a difference either.

I'm doing this on a netbsd-6/amd64 machine.

Is this known lossage?  If so, is this expected lossage?

--chris