In Common Lisp, I believe defpackage is to either define or *redefine* a package.  I've found that in abcl if the package is already defined, defpackage won't redefine it (apparently).
To wit:

CL-USER(2): CL-USER(2): (package-nicknames :utilities) => error package not found
CL-USER(3): (make-package :utilities) ;; so make the package
#<PACKAGE UTILITIES>
CL-USER(4): (package-nicknames :utilities)
NIL ;; has no nicknames
CL-USER(5): (defpackage "UTILITIES"
  (:use "COMMON-LISP")
  (:nicknames "UTIL")) ;; use defpackage to define a nickname
#<PACKAGE UTILITIES>
CL-USER(6): (PACKAGE-NICKNAMES :UTILITIES)
NIL ;;but still no nickname
CL-USER(7): (delete-package :utilities) ;; get rid of the package
T
CL-USER(8): (defpackage "UTILITIES" ;; redefine it
  (:use "COMMON-LISP")
  (:nicknames "UTIL"))
#<PACKAGE UTILITIES>
CL-USER(9): (package-nicknames :utilities)
("UTIL") ;; and it has nicknames
CL-USER(10):

Is this a bug?

Thanks,
Pete