Inconsistence when checking if a pattern is quoted or not for `==' and `=~' in [[ ]]

[Clark J. Wang]

See following script output:

bash-4.2# cat quoted-pattern.sh
[[ .a == \.a* ]] && echo 1  # not quoted
[[ aa =~ \.a* ]] && echo 2  # quoted

[[ aa =~ \a.  ]] && echo 3  # not quoted
[[ aa =~ \a\. ]] && echo 4  # quoted
bash-4.2# bash42 quoted-pattern.sh
1
3
bash-4.2#

>From my understanding 1 2 3 4 should all be printed out.

-- 
Clark