Layer violates LLP_LAYER_16

I am currently trying to understand the Interface between the Loader and a Layer. I found out about [LLP_LAYER_16](https://github.com/KhronosGroup/Vulkan-Loader/blob/master/docs/LoaderLayerInterface.md#requirements-of-well-behaved-layers), which states that vkEnumerateDeviceExtensionProperties must only return its own extensions when pLayerName is specifying the current layer. It seems to me like almost all Khronos layers violate this requirement by appending their extensions to the list of extensions supported by the driver.
Am I understanding something completely wrong?

As an example, the synchronization2 layer does this, probably to mask the fact that the synchronization2 extension is implemented in a layer, but is this allowed by the spec?

I am asking this here instead of in the Loader repo because it is not directly an issue with the loader.