Slight rotation of identical objects

I have an object that consists of 2 objects - one has it's normals facing outward, the second one inwards. They are perfectly aligned in blender, yet upon import, one of them is slightly tilted, for no reason whatsoever, making them not aligned and protruding from one another.

I am aware that Unity has an issue with rotating objects due to different XYZ axis aligment, but why would it alter the rotation of one of the objects without signifying it in the inspector?