By placing skull on ground and trying to place anvil on block beneath skull, action will be cancelled but skull will be reset to default skeleton and turned to default direction. Not shure, it is major or minur bug  but WG or PreciousStones don't prevent this bug so players loss their decorations. 

i couldn't find any plugin or fix to prevent that ;/

Found some informations that there was simillar issue in  SPIGOT-1120 b[ SPIGOT-1120 ]ut i can't fint this issue. 

 

How it works:

https://www.youtube.com/watch?v=Ms8bK71kPcE