Description of problem:
Indexing an Array in Bash is not working as expected

Version-Release number of selected component (if applicable):
bash-4.1.2-40.el6.x86_64

How reproducible:
Always

Steps to Reproduce:
# r=(a b); 
# echo ${r[0]}
a
# echo ${r[1]}
b
# echo ${r[abc]}
a
# echo ${r[---abc]}
b
# echo ${r[---abc]}

#