Steps to reproduce

1. Create the following 'init.vim':

   set nocompatible
   
   let g:n = 0
   inoremap <C-r> <Cmd>let g:n += 1<CR>
   
   nnoremap <M-m> <Cmd>startinsert<CR><Cmd>call complete(col("."), [])<CR>

2. vim --clean -u init.vim

3. Press <M-m>. It starts Insert mode with empty+hidden completion menu.

4. Press <C-r>. It indicates that it waits for a register id. Press a and <Esc> to finish it. Executing :echo g:n shows 0, which means that custom mapping was never used.

5. Start Insert mode with i, press <C-r>, and go back to Normal mode. Executing :echo g:n shows 1, which means that custom mapping was used.

Notes:

• The same behavior is observed if complete() is used with one or more string candidates.
• Custom mapping works as expected if Insert mode completion is started with a built-in mapping. In Insert mode type ab abc a, press <C-n>. This shows a pmenu. Pressing <C-r> does not ask for register and executing :echo g:n later shows increase in g:n value.

Expected behaviour

Custom <C-r> mapping in Insert mode should be executed regardless of whether there is a completion menu shown with complete().

Version of Vim

9.2.316

Environment

OS: EndeavourOS Linux x86_64, 6.19.11-arch1-1
Terminal: Ghostty 1.3.1-arch2
$TERM: xterm-ghostty
Shell: Nu 0.111.0

Logs and stack traces