On build 2494 x64 - workers are not able to use ladders to reach digging zones above ground level anymore.
Screenshot provided: http://www.schubduese.de/2015-07-20_00002.png
Savegame to reproduce: http://www.schubduese.de/saved_games_20150720_2245.7z
Reloading, destroying/rebuilding ladders and so on does not help. Later on this save I tried to reach an ore mine 2 layers above on different mountain layer, does not work - workers just won’t use ladders to dig above.