When removing a shard from a cluster where tags have been assigned to that particular shard, the removeShard admin command will not remove chunks that fall within that tag range.

This is resolvable by removing the shard tag from that shard, and assigning to one (or more) other shards, at which point the balancer takes care of removing the remaining chunks.

I'm not sure if this behavior is intended, but I would have assumed that the removeShard command would "trump" the shard tags.