This is a minor inconvenience since I can inspect the condition and find out what is really going on, but, just thought I would point it out.  From cvs slime (a little out of date).  Anyone else get this behavior?

(defclass test-class ()
  ((a :initarg :a) (b :initarg :b)) )

(defun func1 (lst)
  (declare (type list lst))
  lst )

(defmethod print-object ((obj test-class) str)
  (format str "#<This is an objects special PRINT-OBJECT form ~A ~A>"
          (slot-value obj 'a) (slot-value obj 'b) ))

;; This causes an error (func1 expects a list)
(func1 (make-array 20 :initial-contents
                   (loop for i below 20 collect
                        (make-instance 'test-class :a 1 :b 2) )))

In the debugger I get this (the error message here has lost the "is not of type LIST" part):

The value
  #(#<This is an objects special PRINT-OBJECT form 1 2>
    #<This is an objects special PRINT-OBJECT form 1 2>
    #<This is an objects special PRINT-OBJECT form 1 2>
    #<This is an objects special PRINT-OBJECT form 1 2>
    #<This is an objects special PRINT-OBJECT form 1 2>
    #<This is an objects special PRINT-OBJECT form 1 2>
    #<This is an objects special PRINT-OBJECT form 1 2>
    #<This is an objects special PRINT-OBJECT form 1 2>
    #<This is an objects special PRINT-OBJECT form 1 2> ..)
   [Condition of type TYPE-ERROR]

Restarts:
 0: [ABORT] Return to SLIME's top level.
 1: [TERMINATE-THREAD] Terminate this thread (#<THREAD "repl-thread" {1425AA89}>)

Backtrace:
  0: (FUNC1 #(#<This is an objects special PRINT-OBJECT form 1 2> #<This is an objects special PRINT-OBJECT form 1 2> #<This is an objects special PRINT-OBJECT form 1 2> #<This is an objects special PRINT-OBJECT form 1 2> #<This is an objects special PRINT-OBJECT form 1 2> #<This is an objects special PRINT-OBJECT form 1 2> ...))[:EXTERNAL]
  1: (SB-INT:SIMPLE-EVAL-IN-LEXENV (FUNC1 (MAKE-ARRAY 20 :INITIAL-CONTENTS (LOOP FOR I BELOW 20 COLLECT ...))) #<NULL-LEXENV>)
  2: (SWANK::EVAL-REGION "(func1  (make-array 20 :initial-contents (loop for i below 20 collect (make-instance 'test-class :a 1 :b 2))))
     ")