Slime not showing local variables in :after of mkinstance

Below is the source code snippet for the circular buffer:

(defclass circular-buffer ()
  ((store :accessor store :type vector)
   (head :accessor head :type (integer 0) :initform 0)
   (tail :accessor tail :type (integer 0) :initform 0)
   (granularity :accessor granularity :type (integer 0) :initarg :granularity)
   (charge :accessor charge :type (integer 0) :initform 0))
  (:default-initargs
   :granularity 16))

(defmethod initialize-instance :after ((o circular-buffer) &rest rest &key size granularity)
  (declare (ignore rest) (type (integer 1) size))
  (let ((actual-size (+ (- size (mod size granularity)) granularity)))
    (setf (store o) (make-array actual-size :initial-element nil :adjustable t)
          (charge o) (- actual-size (1+ size)))))

Below is  the SLDB stack trace in slime. The lowest frame does not show any of the actual variables one would expect:

Evaluating call:
  (+ SIZE 1)
With unknown arguments
   [Condition of type SB-EXT:STEP-FORM-CONDITION]

Restarts:
 0: [STEP-CONTINUE] Resume normal execution
 1: [STEP-OUT] Resume stepping after returning from this function
 2: [STEP-NEXT] Step over call
 3: [STEP-INTO] Step into call
 4: [*ABORT] Return to SLIME's top level.
 5: [ABORT] abort thread (#<THREAD "worker" RUNNING {10043AECD3}>)

Backtrace:
  0: ((:METHOD INITIALIZE-INSTANCE :AFTER (CIRCULAR-BUFFER:CIRCULAR-BUFFER)) #<CIRCULAR-BUFFER:CIRCULAR-BUFFER {10049AE8F3}> :SIZE 89 :GRANULARITY 16) [fast-method]
      Locals:
        #:.DEFAULTING-TEMP. = 89
        #:.DEFAULTING-TEMP.#1 = 16
        CIRCULAR-BUFFER::O = #<CIRCULAR-BUFFER:CIRCULAR-BUFFER {10049AE8F3}>
  1: ((LAMBDA (SB-PCL::|.P0.|) :IN "/home/nick/quicklisp/local-projects/trading-core/examples/backtesting-simulation.fasl") #<unavailable argument>)
  2: ((:METHOD INITIALIZE-INSTANCE :AFTER (SIMPLE-MOVING-AVERAGE)) #<SIMPLE-MOVING-AVERAGE {10042040A3}>) [fast-method]
  3: ((LAMBDA (SB-PCL::|.P0.|) :IN "/home/nick/qu