Vines growing on tiles under the claim

[TenPotato]

As far as I know stone tiles decay only if on unclaimed land. A few vines just appeared on my lot, on stone pavement that was made after the land was already claimed.
I can destroy them but some are growing under the palisade, so no way to reach it. I don't want my pavement to disappear(
Is that a bug or something else?