When fences connect sideways, their texture changes and smoothes a bit. This looks disruptive when they connect in different ways. I have screenshots of the original oak fence as well as the dark oak fence and acacia fence. This might be intentional, but it's doubtful.
This is difficult to see in the dark oak fence, but much easier with acacia, for example.
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This MIGHT be a dupe of: MC-66970.