Scrollable Header appears under main items in endlessly scrolling list (rc4)

[shymmq]

I'm initializing the adapter using this code:

adapter.setEndlessScrollListener(this, ProgressItem())
                .setEndlessScrollThreshold(Config.scrollThreshold)
                .setLoadingMoreAtStartUp(true)
adapter.endlessPageSize = Config.pageSize

adapter.addScrollableHeader(AddUsItem())

fragment_post_list_recycler.layoutManager = LinearLayoutManager(activity)
fragment_post_list_recycler.adapter = adapter

and my endless scroll listener looks like this:

override fun noMoreLoad(newItemsSize: Int) = println("All posts loaded")

    override fun onLoadMore(lastPosition: Int, currentPage: Int) {
        viewModel.loadPage(currentPage).subscribe { posts ->
            val postItems = posts.mapIndexed { index: Int, post: Post ->
                val showAd = (index + lastPosition + 1) % adFrequency == 0
                PostItem(post, showAd)
            }
            adapter.onLoadMoreComplete(postItems)
        }
    }

The header always appears under main items, but above progress item.

I have downgraded to v5.0.0-rc3 for now, which seems to have solved the issue.