'completion_auto_change_source' and 'completion_chain_complete_list' select item automatically

[ChrisAmelia]

My testing minimal init.vim

set runtimepath^=~/.local/share/nvim/site/pack/packer/opt/nvim-lspconfig
set runtimepath^=~/.local/share/nvim/site/pack/packer/opt/completion-nvim
set runtimepath^=~/.local/share/nvim/site/pack/packer/opt/vim-vsnip
set runtimepath^=~/.local/share/nvim/site/pack/packer/opt/vim-vsnip-integ

imap <silent> <c-space> <Plug>(completion_trigger)
inoremap <expr> <Tab> pumvisible() ? "\<C-n>" : "\<Tab>"
autocmd BufEnter * lua require'completion'.on_attach()

let g:completion_auto_change_source = 1

let g:completion_chain_complete_list = [
    \{'complete_items': ['path'], 'triggered_only': ['/']},
    \{'complete_items': ['lsp', 'buffers']},
    \{'mode': '<c-p>'},
    \{'mode': '<c-n>'}
\]

lua << EOF
	local lspconfig = require 'lspconfig'
	local root_pattern = lspconfig.util.root_pattern

	local capabilities = vim.lsp.protocol.make_client_capabilities()
	capabilities.textDocument.completion.completionItem.snippetSupport = true

	lspconfig.jdtls.setup{
		root_dir = root_pattern(".git"),
		capabilities = capabilities,
	}
EOF

Description Two issues are happening (although, I believe they are the same?). When the above two options are set:

1. The word being deleted with backspace is automatically completed.
2. Cycling through the completion menu inserts an item automatically (thus preventing from choosing another).

How to reproduce

1. Create file Main.java with:

public class Main {

	public static void main(String[] args) {
		String foo = "Hello, World";
	}

}

2. After line "foo", insert f: a list is suggested: float, foo, for, foreach, fori, ftdetect.

3. Cycle through the suggestions with <Tab>, when passing through foreach, the item is inserted.

Otherwise, it can be reproduced by completing the variable foo., cycle through available methods until the cursor reaches a method with available snippets.

Another issue (maybe with the same origin?): type final, then delete the last character l: the word fina is automatically completed to final.