When breaking chests (or other inventories) next to a wall some of the dropped items sometimes glitch into the wall and fly away.
The more blocks are around the chest, the more likely this is to happen.
The reason this happens is that the positions in which the items get placed can be too close to the sides of the block, which causes the items to stick into the neighbouring blocks.
Steps to reproduce:
1. Place a chest
2. Fill it with items
3. Place blocks all around the chest
4. Break the chest with a command
Some items land outside the box the chest is enclosed in. Expected behaviour would be that all the items are inside the box.
Items that flew through the surrounding chests: