function foo() {
    eval("var a = arguments");
}
foo();

Run the forementioned code and you get an exception:
Uncaught exception - ReferenceError: 'arguments' is not defined

However, if I modify the function foo like this:
function foo() {
    arguments;
    eval("var a = arguments");
}

then the code runs just fine.

This means that the arguments -object (which should be accessible for every function), is not accessible from within eval()'ed code unless it is referenced before the eval().

This is very confusing behaviour, which can lead to really arcane bugs. Unless this behaviour is required for ES5 conformance I suggest to make arguments available inside eval() without prior referencing as one would expect.