It looks to be a loadtime thing (offline Erik thought maybe it was so) See this output:
Armed Bear Common Lisp 0.18.0-dev (built Mon Nov 23 2009 12:07:35 PST) Java 1.6.0_10 Sun Microsystems Inc. Java HotSpot(TM) 64-Bit Server VM Low-level initialization completed in 0.658 seconds. Startup completed in 1.516 seconds. Type ":help" for a list of available commands. CL-USER(1): (jfield "dmiles.TestClass" "StaticField") "fresh" CL-USER(2): (setf (jfield "dmiles.TestClass" "StaticField") "stuff") Debugger invoked on condition of type UNDEFINED-FUNCTION: The function (SETF JFIELD) is undefined. Restarts: 0: TOP-LEVEL Return to top level. [1] CL-USER(3): 0 CL-USER(4): (setf (jfield "dmiles.TestClass" "StaticField") "stuff") Debugger invoked on condition of type UNDEFINED-FUNCTION: The function (SETF JFIELD) is undefined. Restarts: 0: TOP-LEVEL Return to top level. [1] CL-USER(5): :bt 0: (SYSTEM:BACKTRACE) 1: (INVOKE-DEBUGGER #<UNDEFINED-FUNCTION {27F40B69}>) 2: org.armedbear.lisp.Lisp.error(Lisp.java:365) 3: org.armedbear.lisp.SpecialOperators$14.execute(SpecialOperators.java:493) 4: org.armedbear.lisp.Lisp.eval(Lisp.java:461) 5: org.armedbear.lisp.Lisp.evalCall(Lisp.java:501) 6: org.armedbear.lisp.Lisp.eval(Lisp.java:471) 7: org.armedbear.lisp.Lisp.progn(Lisp.java:640) [1] CL-USER(6): 0 CL-USER(7): (setf (jfield "dmiles.TestClass" "StaticField") "stuff") "stuff" CL-USER(8):