[The same bug exists in `with-output-to-string'] A short test case shows the problem. (let (a1 a2) (with-string-as-buffer-contents "foo" (setq a1 (buffer-substring (point-min) (point-max))) (with-string-as-buffer-contents "bar" (setq a2 (buffer-substring (point-min) (point-max)))) (message "a2 = `%s', a1 = `%s', buffer = `%s'" a2 a1 (buffer-substring (point-min) (point-max))))) I see output: a2 = `bar', a1 = `foo', buffer = `' The problem in both functions is that `get-buffer-create' is called with a constant string. Recursive invocations reuse existing buffers and when the recursive call finishes, the outer form's buffer is trashed.