63 items duplicate bug

i have ditributet 63 items in my 9 inv slots. then i brang the items with a double click together. as i opened a chest ...

What I expected to happen was...:
that i have 63 items

What actually happened was...:
i have 63 items and the items from before

Steps to Reproduce:
1. get 63 items of the same type from your creative inventory and hold leftclick to distribute the items in your 9 slots
2. dubble clock on one item of the 9 items to get again 63 items
3. open a chest and you see that there is the 63 item stack and 8 of the item stacks with 7 items

p.s. does also work in survivalmode

Greatings Leon H.-F.