I can reproduce the issue that horizontal and vertical borders rotated by 45˚ appear quite differently with Nearest Neighbor and have so far found no way to rectify it.
What your results are after rotating any picture by 45 degrees in the Nearest Neighbor interpolation mode?
The same mess with Ps 13.0.1 on OS X 10.6.8.
Very interesting that the Free Transform looks good until it is actually commited.
I don't know whether it was different in 13.0
Well, it seems Nearest Neighbor in Photoshop CS5 (12.0.4) provides the same or similar bad results.
I think the term »bad« is justified in this case because considerably different results (aside from the axis) for a 45˚ and a -45˚ rotation seem unexpected and undesirable.
Wow, this is apparently a very old issue.