The bug

If you place a custom player head with a command and then destroy it with setblock or fill in the same tick, the drop is a default player head. However if you place the head with the command, then wait, and then destroy it, the correct drop results.

How to reproduce

1. /setblock X Y Z player_head{Owner:{Name:"seaweed",Id:"4f35f9ed-57e7-417f-97ef-3e4e90b75094",Properties:{textures:[{Value:"eyJ0aW1lc3RhbXAiOjE0NDk0NzAxNDIxMjAsInByb2ZpbGVJZCI6IjRmMzVmOWVkNTdlNzQxN2Y5N2VmM2U0ZTkwYjc1MDk0IiwicHJvZmlsZU5hbWUiOiJPbm5vd2hlcmUiLCJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvOWY5OTc3NjNkNmQ1YzQzYjEzNmU3YWJhYjY2YWU4ZDE5YTdlYzhlMTdkZGExOTRmY2Y5N2U4Yjk3YjRkIn19fQ=="}]}}}

2. In the same tick, and at the same block location run: /fill X Y Z X Y Z air destroy
   → A default player head drops
3. Run the /setblock command again
4. Wait and then run the /fill command
   → Notice the correct player head drops