items not working when in friends world

I was playing minecraft pe with my friend and I was in his world. We were building a house and and was going to need to use stone and glass. Stone was the first on my items that were shown on the bottom and I was able to use it but when I use glass which is on the second it turns into stone so in order for me to use glass I need to make it on the first slot because what I use in all the other slot will become the item in the first slot