Leaves Disappear (Bedrock/PocketEdition)

Hi -

I am attempting to make a tree house but the leaves are decaying and disappearing! All I have done is far is attach blocks to the trees and remove vines since I am working with the large jungle trees. I thought tree leaves only decay if the bottom of the trunk is broken or taken away?  

(I'm sorry if this was duplicated, I was having trouble with finding the topic.)