It was possible to make one way doors using soul sand in some of the earlier versions of Minecraft. While I understand that this was reported as a bug and was fixed in one of the recent updates, I've been using this technique for quite some time, and wasn't aware that it was even considered a bug rather than a feature. The specific details of this change are mentioned as follows https://bugs.mojang.com/browse/MC-3337
I'm not sure if this should be filed under bug or improvement.
I understand that this will probably be filed under 'works as intended' but I'd appreciate if the outcome could be reconsidered.
Like you said, it was a bug, and got fixed, this was never intended behaviour as you were still supposed to be able to enter a 2 high space.
This will most likely not be reconsidered, a workaround can easily be a iron door + one pressure plate