Hi,
Don is correct, the use of the KBI overrides the data direction register on the port.
You want to see the note at the end of chapter 14.5.
To use the part in the way that you describe means that you need to disable the KBI function on that pin with KBIEx = 0, then set the DDR for the pin to output PTADDx = 1.
Now the pin behaves as output.
To go back to KBI, remember so set the GPIO as an input (PTADDx = 0), and re-enable KBIEx = 1.
Mark