title: NSDateFormatter crashes when used from different threads
body: <p>We keep getting a random, weird crash with <code>NSDateFormatter</code>. The relevant stack trace is:</p>
  
  <pre><code>Program received signal:  “EXC_BAD_ACCESS”.
  #0  0x00000005 in ?? ()
  #1  0x0213e3c3 in udat_parse ()
  #2  0x01d4e1ca in CFDateFormatterGetAbsoluteTimeFromString ()
  #3  0x01d4e225 in CFDateFormatterCreateDateFromString ()
  #4  0x003e2608 in getObjectValue ()
  #5  0x003e2921 in -[NSDateFormatter getObjectValue:forString:errorDescription:] ()
  #6  0x003e21cd in -[NSDateFormatter dateFromString:] ()
  </code></pre>
  
  <p>The date formatter is still in memory (i.e. not released or corrupted). The only thing I can think of is the strings upon crash do not conform to the format, but i doubt that will make the formatter completely crash. (it is non trivial to check the format beforehand).</p>
  
  <p>Any thoughts?</p>