This happens at least with two kinds of ladders, one on hunting stands (confirmed by me) and latter on rail cars ( reported by user on reddit: https://www.reddit.com/r/dayz/comments/3conzr/experimental_update_058_of_9th_july_2015/csxqjyy )
This issue is 100% related to 0.58.128665 update, i was able to use all kinds of ladders yesterday. Also, turning -newui off allows mitigation of this issue.