It depends on vim's 'writebackup' option. By default, it's on, but I guess you have it off. You can check in vim with ":set writebackup?" If it returns "writeba

It depends on vim's 'writebackup' option. By default, it's on, but I guess you have it off. You can check in vim with ":set writebackup?" If it returns "writebackup", it's on; if it returns "nowritebackup", it's off. EDIT: Then again, like the other comment mentioned, it seems it also depends on whether the file is in /tmp/. This seems to be because it matches the default pattern in the option "backupskip". For unix, the default is "/tmp/,$TMPDIR/,$TMP/,$TEMP/".