bug#9995: problem about sort -u -k

[夏凯]

when i use sort command with -k and -n together, i got the wrong result:
22:41:21#tp#~> LC_ALL=C
22:41:39#tp#~> /usr/local/bin/sort -u -k1,3 a
1 a q
1 a w
3 a w
22:41:48#tp#~> /usr/local/bin/sort -u -k3 a
1 a q
1 a w
22:41:49#tp#~> cat a
1 a q
1 a w
3 a w
22:41:52#tp#~> /usr/local/bin/sort --version
sort (GNU coreutils) 8.14
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mike Haertel and Paul Eggert.
22:41:57#tp#~>
why is that?
i read http://www.gnu.org/s/coreutils/manual/html_node/sort-invocation.html,
but got nothing about this.
any help is appreciate.
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