What I expected to happen was the lead to stay as it normal does on animals when changing game mode.
Upon changing game mode from normal to peaceful and back the leads on animals in that area had appeared to have despawned. Affected: horses, sheep, dogs(at least). It occurred in Single player.
Steps to Reproduce:
1.In a single player world attract animals to fences via leads.
2.Change game mode to peaceful from normal
3.Change game mode back to normal
4. Repeat until the leads disappear they will be simultaneous.(All slightly random occurance though)