How to switch off Keypad LCD Shield V2.0 -Arduino Compatible


I get this "Keypad LCD Shield V2.0 -Arduino Compatible" from emartee :

I'd like to switch it off to save battery but when I cut off the 5V power attached to VDD of the LCD, the written data on the LCD go off, but the backlight stays on.

It just dim a little. If I unplug RS or EN, it also dim a little more.

Any solution ?

I've been reading on how to switch off LCD when it's alone, and it is said that there is different solution, but to save battery, the best is to cut off main power on VDD.

On my Shield, when I cut off the 5V, I still have 3.50V on VDD
It must get some "back current" from other pin (RS, EN, and D4, D5, D6, D7). How is that possible ?

Here is a schematic I found for the Shield :

I'm full beginner.

Try setting RS, EN, D4, D5, D6, and D7 to LOW in addition to turning off Vdd.

Yes, I've just done this and it switched off completely !

But how is it possible ?
How much current takes the LCD and its backligth on the Arduino pin when the VDD 5V is off ?

Can it destroy the Arduino taking too much current on its pin. I guess it could because the voltage was falling down 3.5V in that case and even more when I unplugged some of D4-D7 or RS, EN to make some test !
Quite scarry !

Is it normal ?