I verified the following bug is there in:

   - sort (GNU coreutils) 8.21
   - sort (GNU coreutils) 8.22
   - sort (GNU coreutils) 8.23

*Input file:*
# cat sort.in
1|a|x
2|b|x
3|aa|x
4|bb|x
5|c|x


*shell command and output:*
# sort -t'|' -k2 <sort.in
3|aa|x
1|a|x
4|bb|x
2|b|x
5|c|x

*I expected that key "a" to come before key "aa" and key "b" to come before
key "bb".*