`org-toggle-item' working as expected.

* org-list.el (org-list-bullet-string): do not modify match-data.
* org.el (org-toggle-item): now working again when changing list items
  into plain text. Moreover take into consideration
  `org-list-two-spaces-after-bullet-regexp'.

lisp/org-list.el

@@ -991,10 +991,11 @@ form (indentation . bullet).  Assumes cursor in item line."
   "Concatenate BULLET with an appropriate number of whitespaces.
 It determines the number of whitespaces to append by looking at
 `org-list-two-spaces-after-bullet-regexp'."
-  (concat
-   bullet " "
-   ;; Do we need to concat another white space ?
-   (when (string-match org-list-two-spaces-after-bullet-regexp bullet) " ")))
+  (save-match-data
+    (concat
+     bullet " "
+     ;; Do we need to concat another white space ?
+     (when (string-match org-list-two-spaces-after-bullet-regexp bullet) " "))))
 
 (defun org-list-replace-bullet (new-bullet)
   "Replace current item's bullet with NEW-BULLET.

lisp/org.el

@@ -17335,21 +17335,21 @@ If the first line is normal text, add an item bullet to each line."
 	  ;; We already have items, de-itemize
 	  (while (< (setq l (1+ l)) l2)
 	    (when (org-at-item-p)
-	      (goto-char (match-beginning 2))
-	      (delete-region (match-beginning 2) (match-end 2))
-	      (and (looking-at "[ \t]+") (replace-match "")))
+	      (skip-chars-forward " \t")
+	      (delete-region (point) (match-end 0)))
 	    (beginning-of-line 2))
 	(if (org-on-heading-p)
 	    ;; Headings, convert to items
 	    (while (< (setq l (1+ l)) l2)
 	      (if (looking-at org-outline-regexp)
-		  (replace-match "- " t t))
+		  (replace-match (org-list-bullet-string "-") t t))
 	      (beginning-of-line 2))
 	  ;; normal lines, turn them into items
 	  (while (< (setq l (1+ l)) l2)
 	    (unless (org-at-item-p)
 	      (if (looking-at "\\([ \t]*\\)\\(\\S-\\)")
-		  (replace-match "\\1- \\2")))
+		  (replace-match
+		   (concat "\\1" (org-list-bullet-string "-") "\\2"))))
 	    (beginning-of-line 2)))))))
 
 (defun org-toggle-heading (&optional nstars)