regular behaviour ?



Sorry for the probable trivial question, I'm an occasional user. I'd 
just like to know if the following behaviour is normal:

(%i1) a[2]:45;
(%o1)                                 45
(%i2) a;
(%o2)                                  a
(%i3) a:[1,2,3];
(%o3)                              [1, 2, 3]
(%i4) a[2];
(%o4)                                 45
(%i5) a[1];
(%o5)                                 a
                                        1

I was expecting something different at least in the 5th output, if not 
in the 4th...