CTRL+\ not working

$ lsb_release -rd
Description: Ubuntu jaunty (development branch)
Release: 9.04

$ apt-cache policy rxvt-unicode-lite
rxvt-unicode-lite:
  Installed: 9.06-1
  Candidate: 9.06-1
  Version table:
 *** 9.06-1 0
        500 http://de.archive.ubuntu.com jaunty/universe Packages
        100 /var/lib/dpkg/status

$ hal-device '/org/freedesktop/Hal/devices/platform_i8042_i8042_KBD_port_logicaldev_input'
udi = '/org/freedesktop/Hal/devices/platform_i8042_i8042_KBD_port_logicaldev_input'
  info.callouts.add = { 'hal-setup-keymap', 'debian-setup-keyboard' } (string list)
  input.keymap.data = { 'e001:fn_esc', 'e009:battery', 'e00a:screenlock', 'e00b:camera', 'e00c:media', 'e00e:dvd', 'e031:help', 'e033:f21', 'e057:wlan', 'e008:presentation', 'e059:help' } (string list)
  input.device = '/dev/input/event4' (string)
  input.product = 'AT Translated Set 2 keyboard' (string)
  info.addons.singleton = { 'hald-addon-input' } (string list)
  input.xkb.rules = 'evdev' (string)
  linux.sysfs_path = '/sys/devices/platform/i8042/serio0/input/input4/event4' (string)
  info.parent = '/org/freedesktop/Hal/devices/platform_i8042_i8042_KBD_port' (string)
  info.subsystem = 'input' (string)
  info.product = 'AT Translated Set 2 keyboard' (string)
  info.udi = '/org/freedesktop/Hal/devices/platform_i8042_i8042_KBD_port_logicaldev_input' (string)
  input.xkb.model = 'pc105' (string)
  info.category = 'input' (string)
  input.x11_driver = 'evdev' (string)
  input.xkb.layout = 'de' (string)
  linux.device_file = '/dev/input/event4' (string)
  input.originating_device = '/org/freedesktop/Hal/devices/platform_i8042_i8042_KBD_port' (string)
  linux.hotplug_type = 2 (0x2) (int)
  info.capabilities = { 'input', 'input.keyboard', 'input.keypad', 'input.keys', 'input.keymap', 'button' } (string list)
  linux.subsystem = 'input' (string)

When I press CTRL+\ the German Umlaut ß is inserted instead, so that I can't detach from dtach with rxvt-unicode-lite. The same is true for xterm and uxterm.