Vimscript infinite loop

Question

I'm trying to combine fzf-bibtex with UltiSnips so that I can search my bibliography file and insert a BibTeX key automatically. I use the following function from fzf-bibtex (which calls the binaries bibtex-cite and bibtex-ls on my system, they just format and output the BibTeX key):

function! s:bibtex_cite_sink_insert(lines)
    let r=system("bibtex-cite ", a:lines)
    execute ':normal! i' . r
    call feedkeys('a', 'n')
endfunction

inoremap <silent> @@ <c-g>u<c-o>:call fzf#run({
                        \ 'source': 'bibtex-ls',
                        \ 'sink*': function('<sid>bibtex_cite_sink_insert'),
                        \ 'up': '40%',
                        \ 'options': '--ansi --layout=reverse-list --multi --prompt "Cite> "'})<CR>

And in my markdown.snippets file I have the following snippet:

snippet q "Quote" i
[$1, $2] $0
endsnippet

If i now press @@ in insert mode when at position $1 after the snipped expanded, it works fine and the fzf prompt with my BibTeX entries is opened.

However, I wanted to automatically call this prompt when the snippet expanded. I thought that could maybe be done with telling vim to just type in @@ when at snippet position $1, so I said:

snippet q "Quote" i
[`!v feedkeys('@@')`, $2] $0
endsnippet

The fzf prompt gets indeed invoked, but it stays in an infinite loop after it entered the selected key, opening the prompt again and again. I can't even quit it with Esc or Ctrl-c.

What did I do wrong? Thanks for helping.