The icomplete-vertical-mode does not list buffer-save-without-query as an option to add-file-local-variable after the input prefix buffer- .

Steps to reproduce
 - emacs -Q
 - switch to buffer bbb, C-x b bbb RET
 - enable completion mode, M-x icomplete-vertical-mode
 - add file local variable, M-x add-file-local-variable abbreviated by
   = M-x add-fi C-j
   = buffer- [does not list completion buffer-save-without-query]
   = alternatives listed are
     - buffer-read-only
     - buffer-offer-save

Expected behavior
 - completion mode lists buffer-save-without-query
   = example of desired completion listing
     - buffer-read-only
     - buffer-offer-save
     - buffer-save-without-query

Unexpected behavior
 - completion mode lists two alternatives without desired option
   = observed completion listing
     - buffer-read-only
     - buffer-offer-save