sounds like what you have is a typical 'double parented' situation. What's happening is that not only are the textures being told to rotate from the eye control, they also inherit a rotation from the head control itself. There are a number of ways to fix this. Some things to try;
1) Instead of parenting the eye control to the head, try giving it a point constraint.
2) Add a statement to the expression that subtracts the head's rotation

There's a couple of other things you can do too, although its been a little too long for me (need to get back to working on stuff...)