Just pulled latest git and did ; reload. I'm running CLISP...

ENDP: A proper list must not end with #<XLIB:WINDOW CLOSED-DISPLAY #x00C00001 #x000334447630>

<1/183> #<SYSTEM-FUNCTION SHOW-STACK> 3
<2/179> #<COMPILED-FUNCTION STUMPWM::PRINT-BACKTRACE>
[178] unwind-protect frame
- #<COMPILED-FUNCTION STUMPWM::BACKTRACE-STRING>
<3/172> #<COMPILED-FUNCTION STUMPWM::BACKTRACE-STRING>
- :TOP-LEVEL
- #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP-1-1>
<4/168> #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP-1-1>
- #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP-1-1>
- #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP>
<5/164> #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP>
- #<SIMPLE-TYPE-ERROR #x000334482D90>
<6/159> #<SYSTEM-FUNCTION SIGNAL> 1
[158] frame binding variables (~ = dynamically):
  | ~ *PRINT-READABLY* <--> NIL
- #<SIMPLE-TYPE-ERROR #x000334482D90>
<7/152> #<SYSTEM-FUNCTION ENDP>
- NIL
- #<COMPILED-FUNCTION STUMPWM::FMT-URGENT-WINDOW-LIST>
<8/147> #<COMPILED-FUNCTION STUMPWM::FMT-URGENT-WINDOW-LIST>
- STUMPWM::FMT-URGENT-WINDOW-LIST
- STUMPWM::FMT-URGENT-WINDOW-LIST
- NIL
- " | BAT: 89% CPU: ^[  5%^]   | "
- #<COMPILED-FUNCTION STUMPWM::FORMAT-EXPAND>
- " | %b %c %t | %u"
<9/137> #<COMPILED-FUNCTION STUMPWM::FORMAT-EXPAND>
- STUMPWM::FORMAT-EXPAND
- " | %b %c %t | %u"
<10/132> #<COMPILED-FUNCTION #:|282 284 (DEFMETHOD MODE-LINE-FORMAT-ELT (#) ...)-42-1-1|>
<11/132> #<STANDARD-GENERIC-FUNCTION STUMPWM::MODE-LINE-FORMAT-ELT>
- ("Sun May 11 09:29:53 PDT 2008")
- STUMPWM::MODE-LINE-FORMAT-ELT
<12/129> #<SYSTEM-FUNCTION MAPCAR>
- CONCATENATE
- #(NIL ((:EVAL (STUMPWM:RUN-SHELL-COMMAND "date | tr -d [:cntrl:]" T)) " | %b %c %t | %u"))
- ((:EVAL (STUMPWM:RUN-SHELL-COMMAND "date | tr -d [:cntrl:]" T)) " | %b %c %t | %u")
<13/122> #<COMPILED-FUNCTION #:|298 310 (DEFMETHOD MODE-LINE-FORMAT-ELT (#) ...)-45-1-1|>
<14/122> #<STANDARD-GENERIC-FUNCTION STUMPWM::MODE-LINE-FORMAT-ELT>
- #<COMPILED-FUNCTION #:|286 293 (DEFMETHOD MODE-LINE-FORMAT-ELT (#) ...)-43-1-1|>
<15/119> #<COMPILED-FUNCTION #:|286 293 (DEFMETHOD MODE-LINE-FORMAT-ELT (#) ...)-43-1-1|>
<16/119> #<STANDARD-GENERIC-FUNCTION STUMPWM::MODE-LINE-FORMAT-ELT>
- #<COMPILED-FUNCTION STUMPWM::MODE-LINE-FORMAT-STRING>
<17/117> #<COMPILED-FUNCTION STUMPWM::MODE-LINE-FORMAT-STRING>
[116] frame binding variables (~ = dynamically):
  | ~ STUMPWM::*CURRENT-MODE-LINE-FORMATTER-ARGS* <--> NIL
- #<COMPILED-FUNCTION STUMPWM::REDRAW-MODE-LINE>
- 
#S(STUMPWM::MODE-LINE :SCREEN #S<screen #<XLIB:SCREEN #x000334447488>> :HEAD #S(frame 0 NIL 0 0 1280 800)
   :WINDOW #<XLIB:WINDOW 1278x17+0+0 localhost #x00C00042 #x00033445EF20> :FORMAT STUMPWM:*SCREEN-MODE-LINE-FORMAT* :POSITION :TOP :CONTENTS NIL
   :CC
   #S(STUMPWM::CCONTEXT :WIN #<XLIB:WINDOW 1278x17+0+0 localhost #x00C00042 #x00033445EF20> :GC #<XLIB:GCONTEXT #x00033445F1A8> :DEFAULT-FG 8355711
      :DEFAULT-BRIGHT 12566463 :DEFAULT-BG 3355443)
   :HEIGHT 19 :FACTOR 781/800 :MODE :STUMP)
<18/109> #<COMPILED-FUNCTION STUMPWM::REDRAW-MODE-LINE>
- #S(frame 0 NIL 0 0 1280 800)
- #<COMPILED-FUNCTION STUMPWM::UPDATE-MODE-LINES>
<19/103> #<COMPILED-FUNCTION STUMPWM::UPDATE-MODE-LINES>
- (#S<screen #<XLIB:SCREEN #x000334447488>>)
- STUMPWM::UPDATE-MODE-LINES
<20/101> #<SYSTEM-FUNCTION MAPC>
<21/98> #<COMPILED-FUNCTION STUMPWM::UPDATE-ALL-MODE-LINES>
- T
- #(NIL "colon")
- "colon"
<22/94> #<COMPILED-FUNCTION STUMPWM::INTERACTIVE-COMMAND>
- "colon"
- 0
- 
(:DISPLAY #<XLIB:DISPLAY localhost:0 (The X.Org Foundation R10400090) X11.0 #x000334447358> :EVENT-CODE 2 :SEND-EVENT-P NIL :SEQUENCE 4795 :EVENT-KEY
 :KEY-PRESS :CODE 115 :WINDOW #<XLIB:WINDOW 1278x798+0+0 localhost #x00E001F4 #x00033444ED88> :EVENT-WINDOW
 #<XLIB:WINDOW 1278x798+0+0 localhost #x00E001F4 #x00033444ED88> :CHILD #<XLIB:WINDOW 1099x635+150+75 localhost #x00E00EF5 #x000334452778> :ROOT
 #<XLIB:WINDOW 1280x800+0+0 localhost #x00000068 #x0003344474B8> :X 669 :Y 408 :ROOT-X 670 :ROOT-Y 409 :STATE 0 :TIME 1227976 :SAME-SCREEN-P T)
<23/90> #<COMPILED-FUNCTION #:G74962>
[86] frame binding variables (~ = dynamically):
  | ~ SYSTEM::*ACTIVE-RESTARTS* <--> 
(#S(RESTART :NAME STUMPWM::QUIT-STUMPWM :TEST #<COMPILED-FUNCTION SYSTEM::DEFAULT-RESTART-TEST> :INVOKE-TAG #:SIMPLE-RESTART-82110 :INVOKE-FUNCTION NIL
    :REPORT #<FUNCTION :LAMBDA (STREAM) (FORMAT STREAM "Quit Stumpwm")> :INTERACTIVE #<COMPILED-FUNCTION SYSTEM::DEFAULT-RESTART-INTERACTIVE>
    :MEANINGFULP T))
- #<COMPILED-FUNCTION STUMPWM::HANDLE-EVENT-2>
<24/79> #<COMPILED-FUNCTION STUMPWM::HANDLE-EVENT-2>
[78] handler frame for conditions (OR XLIB:WINDOW-ERROR XLIB:DRAWABLE-ERROR)
- #<COMPILED-FUNCTION STUMPWM::HANDLE-EVENT-1>
- 99
- 
#(#(NIL
    (:DISPLAY #<XLIB:DISPLAY localhost:0 (The X.Org Foundation R10400090) X11.0 #x000334447358> :EVENT-CODE 2 :SEND-EVENT-P NIL :SEQUENCE 4795 :EVENT-KEY
     :KEY-PRESS :CODE 115 :WINDOW #<XLIB:WINDOW 1278x798+0+0 localhost #x00E001F4 #x00033444ED88> :EVENT-WINDOW
     #<XLIB:WINDOW 1278x798+0+0 localhost #x00E001F4 #x00033444ED88> :CHILD #<XLIB:WINDOW 1099x635+150+75 localhost #x00E00EF5 #x000334452778> :ROOT
     #<XLIB:WINDOW 1280x800+0+0 localhost #x00000068 #x0003344474B8> :X 669 :Y 408 :ROOT-X 670 :ROOT-Y 409 :STATE 0 :TIME 1227976 :SAME-SCREEN-P T))
  #<COMPILED-FUNCTION #:G74962>)
- #<COMPILED-FUNCTION STUMPWM::HANDLE-EVENT>
- #<XLIB:DISPLAY localhost:0 (The X.Org Foundation R10400090) X11.0 #x000334447358>
<25/64> #<COMPILED-FUNCTION STUMPWM::HANDLE-EVENT>
- #<UNBOUND>
- #<UNBOUND>
- #<COMPILED-FUNCTION STUMPWM::HANDLE-EVENT>
<26/61> #<ADD-ON-SYSTEM-FUNCTION XLIB:PROCESS-EVENT> 2
- 1
- #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP-2>
<27/52> #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP-2>
[51] handler frame for conditions ERROR
- #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP-1>
<28/44> #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL-LOOP>
[44] frame binding variables (~ = dynamically):
  | ~ *PACKAGE* <--> #<PACKAGE COMMON-LISP-USER>
[39] frame binding variables (~ = dynamically):
  | ~ SYSTEM::*ACTIVE-RESTARTS* <--> NIL
- #(NIL "")
- NIL
- ""
- ":0"
<29/27> #<COMPILED-FUNCTION STUMPWM::STUMPWM-INTERNAL>
- #<COMPILED-FUNCTION STUMPWM:STUMPWM>
<30/22> #<COMPILED-FUNCTION STUMPWM:STUMPWM>
- #<COMPILED-FUNCTION STUMPWM:STUMPWM>
- ((QUIT))
[10] frame binding variables #<FRAME-POINTER 10> binds (~ = dynamically):
  Next environment: NIL
<31/4> #<FUNCTION :LAMBDA NIL (STUMPWM:STUMPWM) (QUIT)> 0
- #<FUNCTION :LAMBDA NIL (STUMPWM:STUMPWM) (QUIT)>
<32/2> #<COMPILED-FUNCTION EXT::SAVEINITMEM-1>
<33/3> #<SYSTEM-FUNCTION SYSTEM::DRIVER>
<34/3> #<SYSTEM-FUNCTION SYSTEM::DRIVER>
- #<ADDRESS #x000000000000>
- #<ADDRESS #x000000000000>