It might be just a visual effect, as minecart and boat rendered location is significantly behind the actual location. This is probably so the movement looks smooth, so they delay the rendered location to calculate and play movement animation.
After leaving the place and coming again, the lead is now connected to a different place, confirming that this issue is related to loading/unloading leashed mobs
In new snapshot, this can happen during gameplay when a mob is hanged to a happy ghast.
It might be just a visual effect, as minecart and boat rendered location is significantly behind the actual location. This is probably so the movement looks smooth, so they delay the rendered location to calculate and play movement animation.
It is possible that not all spawned there, but rather they walked on the naturally generated haybales and jumped inside the fence.
Trees also generate on roads
[media]Now there are three different bugged leashes on three different spots
After leaving the place and coming again, the lead is now connected to a different place, confirming that this issue is related to loading/unloading leashed mobs