Both set mode and insert in auto-insert-alist lambda

Question

I have the following as a member of auto-insert-alist:

(("/home/robin/.local/bin/.*[^/]\\'" . "Shell-Script mode magic number")
  lambda nil
  (if
      (eq major-mode
          (default-value 'major-mode))
      (progn 
        (sh-mode)
        (insert "#! /bin/bash -peux
# "))))

The mode is set correctly, but the text is not inserted. And it doesn't seem to have been inserted into the wrong buffer, either, because C-x s says "(No files need saving)".