get_immediate echoe character--compiled error?

[richardthiebaud <thiebauddick2@aol.com>]

When I build and run the following program using Gnat 11 in Linux Mint 
21.2, the keys I press are echoed on the console. According to the Ada 
Reference Manual, they should not be echoed. Is this a compiler error?

with ada.text_io; use ada.text_io;
procedure test3 is
   c: character;
   avail: boolean;
begin
   loop
     loop
       Get_Immediate(c, Avail);
       if Avail then
         exit;
       end if;
       delay 0.01;
     end loop;
   end loop;
end test3;	

This does not happen if I call get_immediate without the avail 
parameter, i.e. get_immediate(c);