quit fails to clean up when using multi

~ $ node -v
v10.1.0
~ $ redis-server --version
Redis server v=3.0.6 sha=00000000:0 malloc=jemalloc-3.6.0 bits=64 build=687a2a319020fa42
~ $ lsb_release -a
LSB Version:	core-9.20160110ubuntu0.2-amd64:core-9.20160110ubuntu0.2-noarch:printing-9.20160110ubuntu0.2-amd64:printing-9.20160110ubuntu0.2-noarch:security-9.20160110ubuntu0.2-amd64:security-9.20160110ubuntu0.2-noarch
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.4 LTS
Release:	16.04
Codename:	xenial

Trying to get my head around the redis transaction stuff in order to support atomic events on small (json) objects (ratoms) using watch/multi. The initial code is working but client.quit() doesn't clean up any more:

const newRAtom = (ratom) => {
  const key = getRAtomKey(ratom);
  return new Promise((resolve, reject) => {
    const transaction = client.multi();
    transaction.watch(key);
    client.get(key, (err, value) => {
      if (err) reject(err);
      if (value) reject(key + ' already exists');
      else {
        transaction.set(key, stringify(ratom));
        transaction.exec((err) => {
          if (err) reject(err);
          else resolve(ratom)})}})})};

My theory is that the transaction (multi) ensures that other processes can't create a matching ratom in redis. This works in testing but once the above function has been used client.quit() fails to clean up the client so the javascript tests fail to terminate until -c is used to force an exit. This happens when the newRAtom promise resolves so transaction.exec has been called (and redis monitor shows the expected updates).

Start by reproducing the reported sequence with client.multi(), transaction.watch(), transaction.exec(), and client.quit() on the stated Node.js, Redis, and Ubuntu versions. Trace whether the transaction or watched connection remains active after exec; done means the promise resolves and client.quit() lets the test process terminate without Ctrl-C.