Interesting. I have never heard of such a thing. Seeds know which way to grow independent of light. Fucked up genetics or something!
This is true of all plants - and not just of roots, but of stems too (but the other way around). It's called gravitropism, and simply means that roots will always grow towards the pull of gravity and that stems will grow up away from the pull of gravity. If you tip a straight plant on an angle, the new growth at the stalk will bend upwards, away from gravity, and the taproot will adjust to start going straight down again. Leaves will show phototropism - they grow towards light, but the structural bits of the plant have to consider gravity or they risk growing chaotically such that they topple themselves over.
Check it out :
http://en.wikipedia.org/wiki/Gravitropism
edit: actually, I just read everything above again and I think I misinterpreted - I was thinking that the taproot came out of the top *while* it was upside-down, not before. If the taproot came out of the top of the soil normally then it could just be the case that the seed was planted quite shallow and upsidedown (pointy side of the seed up) - then the taproot has no choice but to go up to get out of the seed, but it immediately turns itself around as it grows out. If it's too close to the top and the seed is upside-down, then sometimes the root can pop out and turn around. The plant should still be fine, though - everything on the seed-side of that loop will eventually emerge and become stem/cotyledon, everything on the other side goes down and stays as root.