Minecraft 1.21.3
Magic 10.9.5-SNAPSHOT-9a873f5
Paper version 1.21.3-76-master@27e4ddc
Was playing with some friends using spells in the Trial Chambers, when suddenly we noticed Wind Charges (thrown by either players or mobs) were destroying/removing blocks upon impact. However, this destruction would then regenerate somehow. I hopped onto my test server to narrow down the bug, and found this:

Casting any spell which has the BreakBlock class in its actions and has an undo parameter, will cause all Wind Charges in the world to cause destructive/block breaking damage. The damage is always a 4x4 square, the blocks are vanished/removed, and then regenerate after the duration defined in the "undo" parameter, and at the speed of "undo_speed". If there is no "undo" parameter, then the blocks don't get destroyed.

Here's a spell you can use to recreate this:

test:
  actions:
    cast:
    - class: BreakBlock
  parameters:
    undo: 10000
    target: other
    range: 0

Just cast this spell, then throw some wind charges at any blocks.