So it is actually possible in every case to use furigana in order to make what kubo writes sounds exactly like spanish? In that case kubo should probably chose to do it perfectly, then again he might chose a certain way because for him it sounds better.
Now you're getting it.
Either Kubo chose the mistakes because he thought they sounded cooler, or because he is ignorant of proper grammar.
Hey, at least he uses better english then most of my classmates XD
No seriously, i always laugh at Kubos titles.
Personal fav is and always will be "Why me sad?"
I think he IS doing it on purpose, he cant be that bad.