EventLog for completed applications always not found if spark.eventLog.compress is true

EventLog for completed applications always not found with following settings in spark-defaults.conf :

spark.eventLog.enabled          true
spark.eventLog.compress         true
spark.eventLog.dir              file:///tmp/spark-events

On Web UI, it shows always "No event logs found for application app-2015xxxxxxx"

but there are files under /tmp/spark-events/ , such as:
app-20151130143343-0000.snappy
app-20151130144008-0001.snappy.inprogress
app-20151130152905-0002.snappy.inprogress
app-20151130153215-0003.snappy