A quick look at the code shows that it pollutes the namespace with undeclared and un-let-bound variables like "tag" (and there could be more like that).

If we investigate further, we might find a culprit like that that's causing this problem.

(defun simple-wiki-get-tag ()

(let (prompt)

(if (and simple-wiki-tag-history (car simple-wiki-tag-history))

(setq prompt (concat "Tag (" (car simple-wiki-tag-history) "): "))

(setq prompt "Tag: "))

(setq tag (completing-read prompt simple-wiki-tag-list nil nil ""

'simple-wiki-tag-history

(car simple-wiki-tag-history))))

(unless (assoc tag simple-wiki-tag-list)

(add-to-list 'simple-wiki-tag-list (cons tag nil)))

tag)