Confused about DSi XL behaviour

Hello, everyone!

So, I wanted to give both my nephews a DS. I got a really good deal on a used DSi XL, so I looked for another used DSi XL so both nephews would have the same version and there would be no fight.

So I've got the two DSi XL here, I'll call one Blue and the other Black. Blue is on version 1.4.1U. Black is on version 1.4U.

I have 3 different flashcarts here: R4iTT (came with Blue), R4i3d (came with the 3DS I bought for myself, a long time ago - never used it) and R4i...

Confused about DSi XL behaviour