Status bar showing caret in split window mode

[rnl16616]

Using NeoVim 0.8
When using a single window the status line shows correctly but when going into split window the status line is filled with the caret (^) symbol - see screenshot. This happens for both a vertical and horizontal split.

I first noticed it a week or so ago when I added in LSP. At first I thought it was just because I was struggling to setup LSP and DAP but now that is done I am still seeing the caret in split window mode. Even if I exclude LSP I still see the caret. I don't often use split windows so I am not sure whether the problem was going to NeoVim 0.8 or something else... If I use nvim -u NONE and split the window the status bar is fine. So it does seem that onedarkpro is the problem. Enabling that causes Lualine to get these carets?

Is there any way to stop this behaviour in Lualine? Or is there a way I can troubleshoot this? It seems there is nothing obviously in the configuration that would cause/allow this behaviour.

lualine.lua is very standard copy/paste with no customisation - just some options set:
local status_ok, lualine = pcall(require,"lualine")
if not status_ok then
vim.notify("Failed to load lualine", lualine)
return
end

lualine.setup {
options = {
icons_enabled = true,
theme = 'onedark',
component_separators = { left = '', right = ''},
section_separators = { left = '', right = ''},
disabled_filetypes = {
statusline = {},
winbar = {},
},
ignore_focus = {},
always_divide_middle = true,
globalstatus = true,
refresh = {
statusline = 1000,
tabline = 1000,
winbar = 1000,
}
},
sections = {
lualine_a = {'mode'},
lualine_b = {'branch', 'diff', 'diagnostics'},
lualine_c = {'filename'},
lualine_x = {'buffers' },
lualine_y = {'encoding', 'filetype'},
lualine_z = {'location', 'progress'}
},
inactive_sections = {
lualine_a = {},
lualine_b = {},
lualine_c = {},
lualine_x = {},
lualine_y = {},
lualine_z = {}
},
tabline = {},
winbar = {},
inactive_winbar = {},
extensions = {}
}

[rnl16616]

OliMorris\OneDarkPro identified a thread with the fix: adding the following snippet to the setup() solved the problem:
highlights = {StatusLine = { bg = "NONE", fg = "NONE" }},