Let's say I have an oven placed inside a town.
If a citizen of that town decides that they want to do some crafting on my oven, when the block 'transforms' the transformed block is now considered MY property.
So this makes it impossible to share an oven with your citizens.
Edit: Meep placed around 100 blocks on my oven and PART of them became his and PART of them became mine. Super odd.
Or as Xerp put it: