That's not how GNU tar behaves.

(Ok, so gnu tar is a lot smarter than standard tar. But standard tar, at least on Solaris, will expand absolute paths...)

Using gnu tar (on cygwin, although it shouldn't matter)

$ mkdir a
$ cd a
$ touch a_file
$ mkdir b
$ cd b
$ touch b_file
$ tar cvf /tmp/abc.tar b_file ../a_file
$ tar cvf /tmp/abc.tar b_file ../a_file
b_file
tar: Member names contain `..'
../a_file
$ tar tvf /tmp/abc.tar
-rw-r--r-- mike/mike      0 2002-04-03 06:48:08 b_file
-rw-r--r-- mike/mike      0 2002-04-03 06:48:02 ../a_file
$ rm b_file ../a_file
$ tar xvf /tmp/abc.tar
b_file
../a_file
tar: ../a_file: Member name contains `..'
tar: Error exit delayed from previous errors
$ ls . ..
.:
b_file

..:
b
[download]

See? The file in .. was not extracted.

Wish I had time to download Archive::Tar to test what it would do, but I have to run to get to work.
--
Mike