Peculiar approx() function in RPN

[PANAMATIK]

The approx() function is well defined and documented for CAS mode and behaves as far as I know here and in Home Algebraic and Textbook modes as expected. A convenient short cut for approx() with only one argument is available with the 'Shift Enter' key. The approx() function with one argument doesn't make sense in Algebraic or Textbook Home Mode, because approximation is done automatically by calculating the result with the 'Enter' function.

However in RPN this key behaves peculiar. When pressing "Shift Enter", an empty bracket appears on the stack. It could represent an empty matrix with 0 elements. Wenn adding a number or doing some other calculation it mutates into empty curly braces, which represent an empty list. I discovered, that the empty Matrix appears only when 'Textbook Display' in Home Settings is activated, otherwise the empty list is created directly on the stack.

When there are, let's say, 4 arguments on the stack 1,2,3,4 entering approx(4) creates a real matrix [1,2,3,4], which cannot be converted into a list.

When there are two numbers on the stack , say 1: 2 and 2: 0.666666666 approx(2) behaves correct and gives the approximated result with 2 digits 1: 0,667.

The 'Shift Enter' Key does clearly have the approx() functionality in RPN mode, which you can see directly, when you press 'Shift Enter' during an error condition.

0 Enter 0 / OK Shift Enter

The text 'approx' like any other function appears in the command line.

But what has an empty list or matrix to do with the approx() function? What is the difference between an empty matrix and an empty list? Can I enter an empty matrix with the brackets key? Does an empty matrix make any sense? Is this functionality intended and I just don't understand it?