weird output from Make

[Yanghui Bian]

Hello all,
I have the Makefile below and it generates weird output:

# --------------------------------
.PHONY: %-test
%-test: %/test
        @echo "sssssssssss"

%/test:
        mkdir -p $*/test
# --------------------------------

$ make 21-test
#mkdir -p 21/test
#sssssssssss
#rm 21/testmake: unlink: 21/test: Operation not permitted

Any clue to the error of the last output line?
If I runs it for the second times, then the error is not there any more
as the
directory is created.
I am using Gnu Make 3.80. 

Thanks.
Yanghui Bian