make world failure: tar/cleaning object tree

Hi,

"make world" fails, "rm -rf /usr/obj ; make -DNOCLEAN world" is fine.

make world failure happens in
--------------------------------------------------------------
>>> stage 2: cleaning up the object tree
--------------------------------------------------------------
...
===> gnu/usr.bin/tar
rm -f tar addext.o argmatch.o backupfile.o basename.o dirname.o error.o
exclude.
o full-write.o getdate.o getline.o getopt.o getopt1.o getstr.o hash.o
human.o mk
time.o modechange.o prepargs.o print-copyr.o quotearg.o safe-read.o
save-cwd.o s
avedir.o unicodeio.o xgetcwd.o xmalloc.o xstrdup.o xstrtoul.o
xstrtoumax.o buffe
r.o compare.o create.o delete.o extract.o incremen.o list.o mangle.o
misc.o name
s.o rtapelib.o tar.o update.o tar.1.gz tar.1.cat.gz
rm: tar: is a directory
*** Error code 1