Query optimizer doesn't use hashed key in a query with sorting on a different indexed value

Hi,

if I execute a query like this:

db.entries.find(

).sort({_id:1})

leads to a full table scan, because he don't use my hashed index on "u.$id".
If I execute with .hint("u.$id_hashed") it works like expected.

See discussion here: https://groups.google.com/d/topic/mongodb-user/ngxI9vkv8Y4/discussion