I have a table, mytable with indexes hash_1__id_1 and hash_1_uid_1.
The shard key of the table is hash_1__id_1.

By executing the following query:
db.mytable.find({'hash' : 1234, 'uid', 1111})
using explain i see that it is actually using the hash_1__id_1 index
instead of the hash_1_uid_1.

Is this because of the fact that hash_1__id_1 is the sharded key?  I
tried to force it to use the other index to see if it is faster as
follows:

db.mytable.find({'hash' : 1234, 'uid', 1111}).hint("hash_1_uid_1")

but that results in an error:

Sat Dec 31 16:03:42 uncaught exception: error: {
        "$err" : "could not initialize cursor across all shards because : bad
hint @ database5/shard5:27018,shard5r:27018",
        "code" : 14827

Is this a problem with my shard key?  Or is there a way around this.

Much appreciated and happy new year!