When I do things in a specific order (coincidentally the one I always do), I can't save a new deck.
My order:
1- Go to slot 10, where I have a saved deck named "_Sketches"
2- Modify that deck, either adding & removing cards or importing a deck code
3- Write a new name in the name box
4- Press the Save button
The new deck isn't created, I don't get the deck as my default deck and my deck in slot 10 didn't change its name.
EDIT: Then I tried saving the deck in slot 9, and got both slots 9 and 10 selected at the same time. Halp