Review the magic minibuffer
Review all the code that goes in to the magic minibuffer in
utilities.el starting at:
;;; ============================================================ ;;; Magic that allows us to clear the initial value in the ;;; minibuffer when the user types a character.
nocompat simplify the advice so it only works in Gnu Emacs. Consider using before-change-functions (mentioned in the comment) instead. There may be an ancient checkin that does this (and that crashed Emacs 20.7).