Cache Stampede Effect in 1.9: If CACHE_TEMPORARY, expire time is left at -1 instead of being set to a time

You can generate near-100% miss rates on certain caches in 1.9 if the entity being cached uses CACHE_TEMPORARY. This means that there is a > 2:1 WRITE TO READ ratio.

Here's the problem:

Notice that in the code below, $expire is not (re-)set until after its value is assigned to $cache->expire.

This seems to result in the behavior that every CACHE_TEMPORARY item expires every time. (See dmemcache_get() for fetching code -- -1 is definitely less than time()).

Furthermore, $expire is never set to the actual expiration time. It is just the number of seconds to wait. The expire time should be variable_get('cache_lifetime', 2591999) + $time

function cache_set($cid, $table = 'cache', $data, $expire = CACHE_PERMANENT, $headers = NULL) {
  $time = time();

  // Create new cache object.
  $cache = new stdClass;
  $cache->cid = $cid;
  $cache->data = is_object($data) ? memcache_clone($data) : $data;
  $cache->created = $time;
  $cache->expire = $expire;
  $cache->headers = $headers;

  // Save to memcache
  if ($expire == CACHE_TEMPORARY) {
    $expire = variable_get('cache_lifetime', 2591999);
  }
  // We manually track the expire time in $cache->expire.  When the object
  // expires, we only allow one request to rebuild it to avoid cache stampedes.
  // Other requests for the expired object while it is still being rebuilt get
  // the expired object.
  dmemcache_set($cid, $cache, 0, $table);
}

I believe this bug should be marked critical, given the fact that it actually hurts overall system performance, rather than helping.