A question on capital and lower-case symbols

Dear Colleagues,

I am still (and, I am afraid, I will remain for a very long time) 
a novice in using Maxima. Please, be so kind to permit me to
ask some questions, probably very naive ones.

Now I cannot understand the output in (D4) (compared to (D2) 
and (D6)) in the Maxima session below (under Windows). I
would prefer that the output would be simply A1.

(C1) a:1;
(D1)         1
(C2) A;
(D2)         A
(C3) a1:2;
(D3)         2
(C4) A1;
(D4)         2
(C5) aa:3;
(D5)         3
(C6) AA;
(D6)         AA

Could you, please, be so kind to help me?

Many thanks in advance and best regards,

Nikos