Hi,
You're getting the right coordinates. Northern hemisphere UTM zones have a Y/northing origin at the equator so any data below there will have negative Y values. Southern hemisphere UTM zones have a Y origin at the equator too, but add a false northing of 10000000 m. That means all Y coordinates in the southern hemisphere will be positive. Points above the equator will have Y values larger than 10 million meters.
Melita