attachedbehaviors

Wpf AttachedBehavior losing base textbox functionalty when using it.

I have a attached behavior issue. When I attach the behavior to my textbox I lose all my base functionality like the Max length? Here is how I am attaching it in my xaml. When I take off the attached behavior the max length work when I put it back on it doesnt work? Any help would be greatly appreciated! This is the class I am usin...