For 3D item models on the hotbar, the viewport is cocked in a pseudo-isometric angle. Specifying "rotation": [ 0, 0, 0 ] (which should imply "no rotation") yields an object that is turned what appears to be 45 degrees to the side and 30 degrees down, instead of head on.
I understand that this pseudo-isometric angle was/is the default for blocks and I don't have a problem with that per se, but making it the hard-coded 'zero point' for all item models is annoying to say the least. These values SHOULD be written in the "/models/item/*.json" files with all of the other translation and scale parameters, instead of making people work out a correction matrix. Coupled with my other bug about rotation being broken (bug MC-72644) it's extremely difficult if not impossible to get things pointed where you want.
Is this still an issue in the current Minecraft Snapshot 15w45a or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.