Well it's more like: Enable backface culling in blender, shows you what the mesh is really like.
So what you should do is:
1) In Blender, enable backface culling
2) Correct all the surfaces that are facing the wrong way
3) Keep going until all surfaces face the correct way
4) Then export
By 'facing the wrong way' I mean a surface that you can not see when you should be able to see it, but you can see it when you are on the wrong side of it. Maybe there is a button or function to flip the direction of a surface (sorry I don't know Blender).
Backface culling is the normal thing for games. It saves the graphics card a lot of work because it doesn't render the triangles that are facing away from you (only needs to draw half the number of triangles). So it's not a bug or anything like that. You just need to make sure the surfaces *are* facing the correct way. The only way to do that is enable backface culling in Blender, as that's how it is when the mesh is drawn in a game.