Intersection between OrientedBoundingBox and BoundingSphere

I am having problems with detecting the intersection between a BoundingOrientedBox and a BoundingSphere.

What I have is a Cylinder spatial representing a building with a BoundingSphere around it. My car is a 3ds model with an OrientedBoundingBox around it. When I get near to the bounds of the BoundingSphere a collision is detected even though I havn't touched the bounding yet.

The effect is as if the BoundingSphere is acting as a BoundingBox for some reason. i.e. if i approach it from the side I can get to touching it before it detects the contact, however if I approach from a corner I am some distance away from the BoundingSphere and it detects a collision.

I have set the debugger to drawBounds so I can see exactly where the bounds are.

Any suggestion how I can fix this?

I have tried applying a BoudingSphere to the car and the collisions then work as expected. Except this is not suitable because the BoundingSphere sticks out a considerable amount to the sides of the car meaning you can't drive closely past it.