Benjamin Whinn originally frustrated with the normal maya mirror tool freezing transforms of -1 scaled objects created the Advanced Mirror Tool for Autodesk Maya as a sort of medium ground between the mirror geometry and duplicate special, with a few other features. The Advanced Mirror Tool for Maya is free, so do it!

“I originally created this script because of my frustrations with freezing transofrms of -1 scale objects and having the opposite node activated and locked. What began as a work-around turned into a journey of mirroring options, and I’m passing the savings on to you!!! Essentially what the Advanced Mirror will do is act as a sort of medium between Mirror Geometry and Duplicate Special, with some added features.”