Here is a Debian bug report (#410060):

From: Peter Baumann <waste.manager@gmx.de>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: xkb-data: ctrl:swapcaps doesn't work (fully) correctly
Date: Wed, 07 Feb 2007 13:10:17 +0100

Package: xkb-data
Version: 0.9-4
Severity: normal

I'm having a strange problem concerning my keyboard setup.

Let me describe:

I have fvwm-crystal installed with 4 virtual desktops and setup a
mapping by <ALT>+<CTRL>+1 do move the active window onto the virtual
desktop 1 (of course, pressing <ALT>+<CTRL>+4 moves the window to
desktop 4).

If I setup my xkb config like this:

  $ setxkbmap -v
  Trying to build keymap using the following components:
  keycodes:   xfree86+aliases(qwerty)
  types:      complete
  compat:     complete
  symbols:    pc(pc105)+us
  geometry:   pc(pc105)

it works as expected. But as I like to have Caps_Lock as an additional
CTRL Key, I run

  $ setxkbmap -layout us -option ctrl:nocaps
  $ setxkbmap -v
  Trying to build keymap using the following components:
  keycodes:   xfree86+aliases(qwerty)
  types:      complete
  compat:     complete
  symbols:    pc(pc105)+us+ctrl(nocaps)
  geometry:   pc(pc105)

and now Caps_Lock behaves like CTRL. I can move my window to every
desktop *except* to desktop 1. That means pressing the keys
<Caps_Lock>+<ALT>+1 does nothing. But pressing <CTRL>+<ALT>+1 behaves as
it should. (so does <Caps_Lock>+<Alt>+2..4)


If I could do anything more specific to resolve this issue feel free to ask.

-Peter Baumann


I don't now if it's usefull, but I attached the output of xev
pressing <CTRL>+<ALT>+1 because <Caps_Lock>+<ALT>+1 had _NO_ output.

  [... snipping uninteresting stuff ...]
  
  KeymapNotify event, serial 15, synthetic NO, window 0x0,
      keys:  4294967218 0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
             0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
  
  KeyPress event, serial 29, synthetic NO, window 0x2400001,
      root 0x4d, subw 0x0, time 2618586448, (-321,-257), root:(780,588),
      state 0x10, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
      XLookupString gives 0 bytes: 
      XmbLookupString gives 0 bytes: 
      XFilterEvent returns: False
  
  KeyPress event, serial 32, synthetic NO, window 0x2400001,
      root 0x4d, subw 0x0, time 2618586469, (-321,-257), root:(780,588),
      state 0x14, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
      XLookupString gives 0 bytes: 
      XmbLookupString gives 0 bytes: 
      XFilterEvent returns: False
  
  FocusOut event, serial 32, synthetic NO, window 0x2400001,
      mode NotifyGrab, detail NotifyAncestor
  
  ConfigureNotify event, serial 32, synthetic YES, window 0x2400001,
      event 0x2400001, window 0x2400001, (1101,845), width 178, height 178,
      border_width 0, above 0x8194ca, override NO
  
  PropertyNotify event, serial 32, synthetic NO, window 0x2400001,
      atom 0x191 (_WIN_AREA), time 2618591573, state PropertyNewValue
  
  FocusIn event, serial 32, synthetic NO, window 0x2400001,
      mode NotifyUngrab, detail NotifyAncestor
  
  KeymapNotify event, serial 32, synthetic NO, window 0x0,
      keys:  2   0   0   0   32  0   0   0   1   0   0   0   0   0   0   0
             0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
  
  KeyRelease event, serial 32, synthetic NO, window 0x2400001,
      root 0x4d, subw 0x0, time 2618591841, (-321,-257), root:(780,588),
      state 0x1c, keycode 64 (keysym 0xffe9, Alt_L), same_screen YES,
      XLookupString gives 0 bytes: 
  
  KeyRelease event, serial 32, synthetic NO, window 0x2400001,
      root 0x4d, subw 0x0, time 2618591850, (-321,-257), root:(780,588),
      state 0x14, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
      XLookupString gives 0 bytes: 



-- System Information:
Debian Release: 4.0
  APT prefers testing
  APT policy: (990, 'testing'), (500, 'unstable')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/bash
Kernel: Linux 2.6.18-3-k7
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)

-- debconf-show failed



Information forwarded to debian-bugs-dist@lists.debian.org, Debian X Strike Force <debian-x@lists.debian.org>:
Bug#410060; Package xkb-data. Full text and rfc822 format available.
Acknowledgement sent to Peter Baumann <siprbaum@stud.informatik.uni-erlangen.de>:
Extra info received and forwarded to list. Copy sent to Debian X Strike Force <debian-x@lists.debian.org>. Full text and rfc822 format available.

Message received at submit@bugs.debian.org (full text, mbox):

From: Peter Baumann <siprbaum@stud.informatik.uni-erlangen.de>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: Re: Bug#410060: xkb-data: ctrl:swapcaps doesn't work (fully) correctly
Date: Fri, 9 Feb 2007 16:25:43 +0100

I could reproduce this behaviour on a etch machine at the university
having a session which only starts xev and no windowmanager.
I get no output for <Caps_Lock>+<Alt>+1 there, too.

There are also some Sun PC's (Opterons) with sun keyboards. On that
machine it works as expected if I run

	setxkbmap -layout us -option ctrl:nocaps

I don't know if the xserver uses a different mapping for those sun
keyboards. Perhaps this gives someone a clue what's wrong.

-Peter Baumann