saving word abbrev file

[J. Blair Amsterdam <JBA at MIT-OZ>]

In Release 5.0 [GC'd Beta Test rev 3], microcode TMC5-MIC 262, FEP 18,
corrected dusty plum, on Lisp Machine Apiary-7 (3600):

I tried to save my word-abbrev file from ZMACS (using M-X Save All
Files, but the same thing happens with M-X Write Word Abbrev File).  

>>Trap: The subscript given to the AR-1 instruction, -2 (from local variable SI:INDEX2), was not a non-negative fixnum.
While in the function %STRING-EQUAL  STRING-EQUAL  ZWEI:WRITE-QWABL

%STRING-EQUAL:  (P.C. = 37)
   Arg 0 (STRING1): "-ABBREV"
   Arg 1 (INDEX1): 0
   Arg 2 (STRING2): "POINT"
   Arg 3 (INDEX2): -2
   Arg 4 (COUNT): NIL

STRING-EQUAL:  (P.C. = 75)
   Arg 0 (STRING1): "-ABBREV"
   Arg 1 (STRING2): ZWEI:POINT
   Arg 2 (IDX1): 0
   Arg 3 (IDX2): -2
   --Defaulted args:--
   Arg 4 (LIM1): NIL
   Arg 5 (LIM2): NIL

ZWEI:WRITE-QWABL:  (P.C. = 45)
   Arg 0 (STREAM): #<FILE-OUTPUT-CHARACTER-STREAM "OZ:PS:<JBA>FOO.QWABL" 34651656>

ZWEI:COM-WRITE-WORD-ABBREV-FILE-INTERNAL:  (P.C. = 10)
   Arg 0 (FN): #<TOPS20-PATHNAME "OZ:PS:<JBA>FOO.QWABL">

ZWEI:COM-SAVE-WORD-ABBREV-FILE-INTERNAL:  (P.C. = 40)
   Arg 0 (WHEN): :ASK

ZWEI:COM-SAVE-ALL-FILES:  (P.C. = 71)

ZWEI:COM-EXTENDED-COMMAND:  (P.C. = 27)

ZWEI:COMMAND-EXECUTE:  (P.C. = 55)
   Arg 0 (COMMAND): ZWEI:COM-EXTENDED-COMMAND
   Arg 1 (CHAR): 1130
   Arg 2 (PREFIX-CHAR): NIL
   Arg 3 (HOOK-LIST): (ZWEI:RETURN-TO-PREVIOUS-CONTEXT-HOOK-FUNCTION ZWEI:EXPAND-ABBREV-HOOK ZWEI:SHIFT-LOCK-HOOK)

Rest of stack:
ZWEI:PROCESS-COMMAND-CHAR:  (P.C. = 14)
(:METHOD ZWEI:EDITOR :EDIT):  (P.C. = 200)
(:METHOD ZWEI:TOP-LEVEL-EDITOR :COMBINED :EDIT):  (P.C. = 41)
ZWEI:ZMACS-WINDOW-TOP-LEVEL:  (P.C. = 16)
SI:PROCESS-TOP-LEVEL:  (P.C. = 53)