First off, you should not be modifying DT_INTS-14.
It even says so in the code that you modified.
The changes that you made were incorrect (see the comments in DT_INTS-14), but I don't think they would have affected EE_Vars.

Since I cannot duplicate your problems with the same hardware and software, I can't agree that there is a problem with EE_Vars.
It all works perfectly here.

You don't have any way to debug your program/hardware, no LCD, the USART pins are used for other purposes.
So you are left to make guesses on what is happening, and I can't ask you to check register values.
Naturally, those guesses point blame at everything you didn't do. It's human nature.

I would recommend building in some form of debugging capabillity in your next project.
A serial LCD that only uses one pin can be extremely usefull.

With that said, there have been many changes to PBP since I wrote EE_Vars, and much of it's functionality is now included in the compiler.
So there's not much reason to use EE_Vars anymore.