We've been bitten before (SERVER-19392, SERVER-27362, SERVER-24704) by the helper class AutoGetCollectionForRead doing more than intended, and perhaps default to use the helper too often. Within the pipeline directory, we use this helper frequently within stages like $out, $collStats, $lookup, etc. We should make sure these usages aren't doing more than intended by the author, and correct any accidental side-effects such as updating top, changing the operation's namespace as reported by currentOp, etc.