Neovim version (nvim -v)

NVIM v0.7.0

Vim (not Nvim) behaves the same?

no, vim 8.0 1-1763

Operating system/version

Rocky 8.5

Terminal name/version

kitty 0.23.1

$TERM environment variable

xterm-256color

Installation

system package manager

How to reproduce the issue

set backup
set backupdir=.backup/,~/.vim-backup/backup//,/tmp//

$ cd tmp/; mkdir -p a b; touch a/foo; ln -fs ../a/foo b/foo
$ nvim a/foo # do some edit, write, edit, write
$ ls ~/.vim-backup/backup/
%home%jerome%tmp%a%foo~
$ nvim b/foo # do some edit, write

Expected behavior

Write succeeds

Not sure about the behavior, but I would like something like

$ ls ~/.vim-backup/backup/
%home%jerome%tmp%a%foo~
%home%jerome%tmp%b%foo~

vim 8.0 behavior is not an example, as it does not support complete path backup name with %

Actual behavior

When I write in neovim, I get an error:

:w
E506: Can't write to backup file (add ! to override)