How to reproduce:
Type "10 september" into the expiry box on Special:Block (if this date has passed, increase it)
Go back to the log entry for that block, and you see a year of 1970.
Expected result: Year should be 2013
09:17, 8 September 2013 Legoktm (talk | contribs | block) blocked Legosock (talk | contribs) (autoblock disabled) with an expiry time of 00:00, 10 September 1970 (testing a bug) (unblock | change block)
Note that this doesn't affect the actual block, which uses the intended expiry. This can be confirmed by looking at [[Special:BlockList]] (https://en.wikipedia.org/wiki/Special:BlockList?wpTarget=Legosock&limit=50) or via the API: https://en.wikipedia.org/w/api.php?action=query&list=logevents&letype=block&lelimit=100&format=jsonfm&letitle=User:Legosock