This behavior was only introduced in 14w30a.
Normally, you can walk up stairs as long as you are moving towards them. However, because of this bug, when a block is in a certain location, you are unable to walk up stairs unless you are looking in the direction they are facing.
I made a quick video to show the bug in action because it is difficult to explain. http://youtu.be/ywTSkQtiltk
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migrated
migrated
Yeap just noticed this problem. Also happens with torches and it's even worse with them
qmagnet
Duplicate of MC-61245
Sorry, this isn't actually a duplicate. It doesn't matter if the stairs were placed before 14w30b, and you can break blocks through the holes in the stairs just fine. That is a completely different bug from what I can tell. Please reopen.