Unsure if I was doing this wrong or if this is bugged, using right trigger punches and doesn't place chest on the donkey (as some say to), left trigger either rides the donkey/goes into it's inventory when crouched.

Most recent update for bedrock edition (phase 1 of aquatic, unsure if present in beta for  1.5.0.4) 

Donkey is tamed.

Video of issue.