WITH default binding for typed variables

[Bike]

(loop with *package* = (find-package whatever)) expands into

(BLOCK NIL
  (LET ((*PACKAGE* NIL) (#:FORM542 (FIND-PACKAGE WHATEVER)))
    (DECLARE (IGNORABLE *PACKAGE*))
    (SETQ *PACKAGE* #:FORM542)
    (TAGBODY
     #:BODY543
      (GO #:BODY543)
     EPILOGUE
      (RETURN-FROM NIL NIL))))

i.e. it binds the variable to nil and then sets it. For a fresh lexical variable this is no problem, but *package* has to be a package, and binding it to a non-package has undefined consequences. On SBCL and Clasp it is an error. There would be a similar problem for any variable declared to have a type not including nil.