When a variable’s custom-form is 'lisp (or 'mismatch),
`custom-variable-value-create' will quote its value prior to storing it
inside the widget.  Afterwards, `custom-variable-modified-p' will try to
compare this quoted form to the (unquoted) value and think that the
variable has been modified.

To reproduce, fire up emacs -Q and do:

  1. (setq custom-variable-default-form 'lisp)
  2. M-x customize-variable RET auto-save-file-name-transforms RET

You will notice that Customize thinks that the variable has been
modified even though that is not true.  If step 1. is omitted,
everything is fine.

The patch attached below fixes that.