Problem with unbounded string input

[Brian McGuinness <b.mcguinness747@gmail.com>]

I was having trouble reading unbounded strings, so I wrote a short test program and had the same problem.

with Ada.Strings.Unbounded;
with Ada.Text_IO;
with Ada.Text_IO.Unbounded_IO;

procedure scan2 is
  use Ada.Strings.Unbounded;
  line : Ada.Strings.Unbounded.Unbounded_String;
begin
  loop
    Ada.Text_IO.Put ("-> ");
    line := Ada.Text_IO.Unbounded_IO.Get_Line;
    exit when line = "quit";
    Ada.Text_IO.Unbounded_IO.Put_Line ("""" & line & """");
  end loop;
end scan2;

When I compile this with gnatmake 8.3.0 under Linux Mint Debian edition 4 and run it, every so often when I type a line and hit Enter there is no response until I hit Enter again, and then everything typed before the first Enter is ignored.  The rest of the time the lines I type are read and returned correctly.  I am really puzzled by this.  Is this a bug in the Ada library or am I doing something wrong?

--- Brian McGuinness