Nether fortress bounding boxes in 1.8 vanilla and latest Forge for 1.8 are not the same - the structure data that forge is showing is different than in the fortress.dat file.
In this particular example it's a fortress that was generated in 1.6.2, then the world was updated to 1.7.2 so the fortress.dat file contains the 1.7.x bounding boxes and don't line up with the blocks. In 1.8 Vanilla it shows the correct bounding boxes:-
https://pbs.twimg.com/media/B_-ykjVVEAEX0W4.png[/img]
However in Forge 11.14.1.1337 (and several earlier versions) the bounding boxes look like they were generated fresh in 1.8.
https://pbs.twimg.com/media/B_-ykb6VAAARz9e.png[/img]