Use proper method for accessing fields

[mrsylerpowers]

You are unable to override the fields method fully if this method is not used here

[matijakolaric]

Hi, and thanks. I will be back early next week and have a look at this. I did a brief test, and the bug exists.

I think this will work, but I want to test it properly.

What you are using this for?

[mrsylerpowers]

I am overriding this to make fields an instance variable instead of a class variable so that variable-length fields are supported. Using a deep copy of _fileds as an instance variable allows for the sizes of the fields to be changed on an instance basis.