Steps to reproduce: 

1. create a world.
2. add to your world a behaviour/resource pack.
3. open your world settings
4. goto "Resource Packs" tab and enable "Require players to accept resource packs to join"
5. Open the World.
6. join this world with another device.
7. will popup "Download World Resource Packs?"
8. click "Leave"

Observed results: 

" Downloading packs [0 / 0] " GUI remains, untill I click "Cancel"(I wait only 10 seconds).