What I expected to happen was...:
items spill out of invetory as if dropped
What actually happened was...:
items instantly despawned
Steps to Reproduce:
1. fill inventory
2. type /give @p {item}
Linked issues
Comments

Thank you for your report!
We're actually already tracking this issue in MC-8409, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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not sure if this was added a feature but i remember items spilling out of the players inventory with a command block running