using format to write to a string

[<@IU.AI.SRI.COM:slug-admin@iu.ai.sri.com>]

    Date: Fri, 26 Jun 1992 06:17 EDT
    From: starnet!bass!lakin@apple.com (Fred Lakin)

    Seems to work for me on a 36xx [as well as in unix CL's], 
    but not on an XL400.

    Am I doing something wrong here?

[...]

    Command: (defun test-io-to-string (&aux keep-string)
	       (setf keep-string (make-array 0 :element-type 'STRING-CHAR
					       :fill-pointer 0 :adjustable T))
	       (format keep-string "Here we see ~A happen " 'BIG-BLOWUP)
	       keep-string)
    TEST-IO-TO-STRING
    Command: (test-io-to-string)

    Trap: The word #<DTP-FIXNUM 14534462510> was read from location 1232731 
     (in WORKING-STORAGE-AREA).

By the way folks, don't try this at home.  This is one of those nasty
bugs that leaves a little land-mine in your memory that will take you
directly to the FEP at some unspecified later time...

I've taken the liberty of passing on a bug report, but as Guy pointed
out, leaving out the :adjustable argument is a work-around.