Buffer Append Graphical Oddity

[starcraftman]

Hello, I was investigating porting the vim-plug python installer to neovim for a fallback. I've made it work on neovim & vim but there is an odd buffer difference. I've made a gif to demonstrate, you can see that the entries jump up & down a level at a time randomly. This doesn't happen with vim. You can see expected behaviour gif at https://github.com/junegunn/vim-plug .

To reproduce:

1. Clone my fork of vim-plug git clone -b nvim_py https://github.com/starcraftman/vim-plug .Note: I've hard disabled neovim & ruby on this branch to ensure python executed.
2. Replace normal plug.vim with my fork.
3. Use any config of vim-plug with nvim, for example: https://raw.githubusercontent.com/starcraftman/.my_scripts/master/dot_files/.vimrc

Not a high priority, but definitely jarring.

Edit: So you don't have to search the big file, the code manipulating the buffer: https://github.com/starcraftman/vim-plug/blob/nvim_py/plug.vim#L1065-L1128