Surprising behaviour of strings.fixed.overwrite

["Markus Schöpflin" <no.spam@spam.spam>]

Given the following Ada program:

---%<---
with TEXT_IO;
with ADA.STRINGS;
with ADA.STRINGS.FIXED;

procedure TEST
is
    S : STRING(1 .. 6);
begin
    S := "@@@@@@";
    ADA.STRINGS.FIXED.OVERWRITE (S, S'First + 5, "56", ADA.STRINGS.LEFT);
    TEXT_IO.PUT_LINE (S);

    S := "@@@@@@";
    ADA.STRINGS.FIXED.OVERWRITE (S, S'First + 5, "56", ADA.STRINGS.RIGHT);
    TEXT_IO.PUT_LINE (S);
end;
--->%---

What would you expect to be the output of the program?

Scroll down for the answer...

















































Well, I would have expected the output to be

@@@@@6
@@@@@5

But it is:

@@@@56
@@@@@5

Which is correct according to the definition of overwrite, but nevertheless I 
find this extremely surprising.

Am I alone in this?

Or can anyone please the rational on defining the behaviour of overwrite as it is?

Markus