Edited as issue was resolved.
As I read other stair-related bug reports, I guess this behavior might be a result of the hitbox problem with stairs so the stair can't be attached to each other because it might think the stair faces the wrong direction for that or it is not a stair at all, not sure about that though.
I can confirm this on Windows 8.1 x64 using Java 1.8.0_11 (x64).
it wouldn't let me put version 1.6.1 on the "version indicator"
For zerfit: 我正在使用翻译器,但请查看具有类似问题的另一个线程......MCL-18214 我重新安装了对我有用的。
For Jan: check out the other thread with similar issue... I did a re-install that worked for me. (MCL-18214).