When a feature is added to the model, like for instance a hole, it is mirrored in real time on the other side or other half of the model as well, as a mirror feature function constantly is on. In a particular case it behaves like the X-Z plane is a mirror.
What is going on?
Solution
There is a display function called Mirror Display that constantly show all you do mirrored through a plane in real time when you do it. It is designed to be used when modeling half of a symmetric model to aid in visualizing the final shape.
So the feature action is not mirrored, it is just the display of it.
If you do not want this behavior, please try and toggle it off under Menu -> View -> Operation -> Mirror Display
Notes and References
Hardware/Software Configuration
Platform: INTL64
OS: window
OS Version: 1064
Product: NX
Application: STUDIO_DESIGN
Version: V12.0.2
Function: ANALYZE
Ref: 001-9484425