Balanced/Unbalanced switch action on MC302 amplifier (or similar)

[LazyBorzoi]

I got a question for owners of MC302 or similar Mc amplifiers that have a switch on the back that allows switching between balanced and unbalanced input connections.

(1) If I connect to the amp using unbalanced cables (RCA) and keep the switch in unbalanced position, I get one volume. If I then flip that switch to balanced position but keep the same cables, the music still plays but the volume slightly goes down. To be honest, I don't understand why I still hear the music - shouldn't it completely switch to the balanced inputs which in my case are not wired???

(2) Then I removed the RCA cables and replaced them with balanced cables (XLR). In this case, I still hear the music in both positions of the switch (balanced or unbalanced) but the volume doesn't change like it did in case (1).

If you have MC302 or another Mc amp that has balanced/unbalanced switch, could you please verify/confirm that what I see is a normal behavior?
Thanks in advance!