Items that are dropped form a shulker box can be picked up instantly. Normally when you drop an item, you need to wait for a bit to pick it up.

To reproduce

1. Fill a shulker box with various items (type does not matter)
2. Stand directly above lava
3. Throw the shulker box into lava
   → You can pick up the contents of the shulker box immediately

Video

Minecraft 20w51a - Singleplayer 2020-12-16 18-38-06.mp4