Is it possible that we are only seeing a snapshot of a very transient phase in this particular system? Perhaps within a few thousand years the instability of this arrangement will become apparent with, say, two of the planets colliding, or one being absorbed by the star?
Another possibility is that as we look around the universe we find arrangements that throw our notions of sytem 'normality' out the window. For example, perhaps these planets have a synchronised or 'locked' orbit similar to the inner moons of Jupiter....

Questions I would also ask:
- what's the mass of the star? If it's small, perhaps the collected mass of the planets works in some sort of binary way, with the centre of gravity lying between the star and the inner planet, or on the outside edge of the star?

- and, finally, if it really is a highly unstable arrangement, are we 99% sure the data is being interpreted correctly?

This is all just idle speculation, but it's fun eh...! With a bit of luck a professional astronomer (perhaps one from this show) will provide an answer now... :-)