bug ? 2 static pages whith the same post name are display together

Hello,

I was working on my permalinks to make them the more intuitive and I have found something like a bug (I guess / I hope it’s not and to learn) :

When 2 pages have the same post name, even they aren’t in the same place in the child structure, the are display in the same page !

Example : 2 pages with post name : “good-stuff” in 2 different places of the structure of pages will be display in the same post ! …

How to keep my simple names and correct this phenomenon ??