Geometry Manipulation Issues

greetings all - I'm thrilled to finally be among fellow graphic artists and i have a problem I'd like to resolve.

I've somehow stumbled upon a feature that i can't identify or turn off. it's a feature that mirrors geometry along a central axis. On creating any primitive, when selecting a vertex, a face or edge; the geometry being manipulated is mirrored at it's opposite side. For example, this first occurred while manipulating a NURBS plane; on selecting a vertex, i notice that a vertex at it's opposite (in the same mesh, of course), shaded white, would mimic any manipulation i made upon my orriginal selection. I've tried turning the caps lock off, restarting the program, deleting history, freezing transformations, resetting my preferences and restarting my computer. Where is this mirroring feature located so i may turn it off? Please... I have little hair left.

Double click on the Move Tool in the Toolbox and turn off reflection in the Reflection settings.

Excellent! Thank you very much.