Major - P3 Filing as a bug since greg_10gen thinks this should be caught by mongos before forwarding command to shards.
Collection name is "unsharded.errors.$foo". As the db name implies, this is to an unsharded DB.
2.6 mongos with 2.6 shards:
{ "ok" : 0, "code" : 2, "errmsg" : "invalid collection name at shard0000" }
2.6 mongos with 2.4 shards:
{
"ok" : 1,
"n" : 0,
"writeErrors" : [
{
"index" : 0,
"code" : 10093,
"errmsg" : "cannot insert into reserved $ collection"
}
]
}