Why does Tab select the second item in the completion list?

[linw789]

I configured nvim-cmp to work with rust lsp. But for some reason pressing tab selects the second item in the completion list. In the example below, when I press tab, position_1 is selected instead of position_0.

What might have I missed configured?

This is my nvim-cmp config:

local cmp = require('cmp')
local luasnip = require('luasnip')

local select_behavior = { behavior = cmp.SelectBehavior.Insert }
cmp.setup({ 
  snippet = { expand = function(args) luasnip.lsp_expand(args.body) end },
  completion = { autocomplete = {cmp.TriggerEvent.TextChanged} },
  sources = { 
    { name = 'buffer', keyword_length = 2 },
    { name = 'nvim_lsp', keyword_length = 2 },
    { name = 'path', keyword_length = 2 },
  },
  window = { documentation = cmp.config.window.bordered() },
  mapping = {
    ['<Tab>'] = cmp.mapping(function(fallback)
      if cmp.visible() then
        cmp.select_next_item(select_behavior)
      else
        fallback()
      end
    end, {'i', 's'}),
    ['<S-Tab>'] = cmp.mapping(function(fallback)
      if cmp.visible() then
        cmp.select_prev_item(select_behavior)
      else
        fallback()
      end
    end, {'i', 's'}),
  }
})