Comment 2 for bug 1349528

This seems to be a bug in radosgw. For an ugly workaround, something like this could help

584,585c584,589
< utc = gmtime(float(meta.get('x-timestamp')))
< datestamp = strftime('%Y-%m-%d %H:%M:%S', utc)
---
> timestamp = meta.get('x-timestamp')
> if timestamp is None:
> datestamp = '????-??-?? ??:??:??'
> else:
> utc = gmtime(float(timestamp))
> datestamp = strftime('%Y-%m-%d %H:%M:%S', utc)

For nicer workaround, there could be iteration over existing object to find the latest modification. But I'm not sure it's worthy.