copper golems sometimes place items into random chests even though there is a chest with that item already

Thank you for your report!
However, this issue is Working as Intended.

The report you have submitted is working as intended: from the 1.21.100.23 Preview changelog

• It can place an item in a Chest if it's empty, or if it contains the same type of item it is holding in its hand

• The Copper Golem will visit max 10 Chests or Copper Chests in sequence to try to pick up or place an item.

"In sequence" refers to the chests proximity to the copper chest, or the order in which the copper golem detected them. There is no mechanic to prioritize chests with items stated in the changelog.

Please note, that mechanics of the game may change between updates.
Things such as graphics, sounds, world creation, biomes, redstone, villagers, and animals may not work the same in current versions.

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