/usr/src -> make doesn't recognize target when '-f -' is used

[rank1seeker at gmail.com]

cd /usr/src

This works:
--
# echo 'CPUTYPE?=core2
CFLAGS+=-march=native
NO_CPU_CFLAGS=yes
COPTFLAGS+=-march=native
NO_CPU_COPTFLAGS=yes' | /usr/bin/make __MAKE_CONF=/dev/null -f - -V CPUTYPE
--

This DOESN'T:
--
# echo 'CPUTYPE?=core2
CFLAGS+=-march=native
NO_CPU_CFLAGS=yes
COPTFLAGS+=-march=native
NO_CPU_COPTFLAGS=yes' | /usr/bin/make __MAKE_CONF=/dev/null -f - -j4 buildworld

make: don't know how to make buildworld. Stop
    (Yes, in /usr/src)
--

When '-f -' is removed, build will start?
Is this a bug or I simply don't see, an obvious thing?


Domagoj Smolčić