The 'double leap second' issue has been around a long time and is part
of the Posix standard (for some background see
http://www.ucolick.org/~sla/leapsecs/onlinebib.html, specifically the
section named 'Unix system time and the POSIX standard').  This document
notes that the double leap second was still in the standard in 1997, and
according to Wikipedia that is after the last revision of the standard,
so presumably it is still there.

Therefore the time documentation of strftime is correct, since my
understanding is that time is a wrapper around the Posix time functions.
 The datetime docs, on the other hand, are misleading in the strftime
documentation.  I've attached a doc patch to have the note clarify that
datetime does not consume or produce leap seconds.