tar dumps core when appending to empty file

What I am trying to do is:

$ touch Makefiles.tar
$ find . -name Makefile.orig -exec tar -r -f Makefiles.tar {} \;

This causes tar to dump core as fast as find can find the specified files.

So I tried:

$ touch Makefiles.tar
$ tar -r -f Makefiles.tar Makefile.inc1

And also got a core dump.  I then tried:

$ tar -c -f Makefiles.tar Makefile.inc1
$ find . -name Makefile.orig -exec tar -r -f Makefiles.tar {} \;

This worked as I expected.

I seem to have uncovered a bug.  It seems reasonable to me to append to an 
empty file.  Perhaps I am missing some sort of arcana here.

Later,
Jason C. Wells