That is a bug for xdg-open. Jiajun is using xdg-open 1.0.1. On my Ubuntu 10.10 x86_64, the version of xdg-open is 1.0.2 and I don't have that issue.

Here is the diff between two xdg-opens.

--- /usr/bin/xdg-open.orig      2010-03-11 23:54:02.000000000 -0800
+++ /usr/bin/xdg-open   2012-04-18 20:42:18.341913133 -0700
@@ -200,7 +200,7 @@
 }

 #------------------------------------------------------------
-# Exit script on insufficient permission to read a specified file
+# Exit script on insufficient permission to write a specified file

 exit_failure_file_permission_write()
 {
@@ -277,7 +277,7 @@
             ;;

             --version)
-            echo "xdg-open 1.0.1"
+            echo "xdg-open 1.0.2"
             exit_success
             ;;
         esac
@@ -303,7 +303,8 @@
 {
     if [ x"$KDE_FULL_SESSION" = x"true" ]; then DE=kde;
     elif [ x"$GNOME_DESKTOP_SESSION_ID" != x"" ]; then DE=gnome;
-    elif xprop -root _DT_SAVE_MODE | grep ' = \"xfce4\"$' >/dev/null 2>&1; then DE=xfce;
+    elif `dbus-send --print-reply --dest=org.freedesktop.DBus /org/freedesktop/DBus org.freedesktop.DBus.GetNameOwner string:org.gnome.SessionManager > /dev/null 2>&1` ; then DE=gnome;
+    elif xprop -root _DT_SAVE_MODE 2> /dev/null | grep ' = \"xfce4\"$' >/dev/null 2>&1; then DE=xfce;
     fi
 }

@@ -314,7 +315,7 @@

 kfmclient_fix_exit_code()
 {
-    version=`kde-config --version 2>/dev/null | grep KDE`
+    version=`kde${KDE_SESSION_VERSION}-config --version 2>/dev/null | grep KDE`
     major=`echo $version | sed 's/KDE: \([0-9]\).*/\1/'`
     minor=`echo $version | sed 's/KDE: [0-9]*\.\([0-9]\).*/\1/'`
     release=`echo $version | sed 's/KDE: [0-9]*\.[0-9]*\.\([0-9]\).*/\1/'`
@@ -324,12 +325,25 @@
     return 0
 }

-open_kde()
+# This handles backslashes but not quote marks.
+first_word()
 {
-    which kfmclient >/dev/null || open_generic "$1"
+    read first rest
+    echo "$first"
+}

-    kfmclient exec "$1"
-    kfmclient_fix_exit_code $?
+open_kde()
+{
+    if kde-open -v 2>/dev/null 1>&2; then
+        kde-open "$1"
+    else
+        if [ x"$KDE_SESSION_VERSION" = x"4" ]; then
+            kfmclient openURL "$1"
+        else
+            kfmclient exec "$1"
+            kfmclient_fix_exit_code $?
+        fi
+    fi

     if [ $? -eq 0 ]; then
         exit_success
@@ -340,7 +354,11 @@

 open_gnome()
 {
-    gnome-open "$1"
+    if gvfs-open --help 2>/dev/null 1>&2; then
+        gvfs-open "$1"
+    else
+        gnome-open "$1"
+    fi

     if [ $? -eq 0 ]; then
         exit_success
@@ -360,38 +378,73 @@
     fi
 }

+open_generic_xdg_mime()
+{
+    filetype=`xdg-mime query filetype "$1" | sed "s/;.*//"`
+    default=`xdg-mime query default "$filetype"`
+    if [ -n "$default" ] ; then
+        xdg_user_dir="$XDG_DATA_HOME"
+        [ -n "$xdg_user_dir" ] || xdg_user_dir="$HOME/.local/share"
+
+        xdg_system_dirs="$XDG_DATA_DIRS"
+        [ -n "$xdg_system_dirs" ] || xdg_system_dirs=/usr/local/share/:/usr/share/
+
+        for x in `echo "$xdg_user_dir:$xdg_system_dirs" | sed 's/:/ /g'`; do
+            file="$x/applications/$default"
+            if [ -r "$file" ] ; then
+                command="`grep -E "^Exec(\[[^]=]*])?=" "$file" | cut -d= -f 2- | first_word`"
+                command_exec=`which $command 2>/dev/null`
+                if [ -x "$command_exec" ] ; then
+                    $command_exec "$1"
+                    if [ $? -eq 0 ]; then
+                        exit_success
+                    fi
+                fi
+            fi
+        done
+    fi
+}
+
 open_generic()
 {
-    # If it's a path or a file:/// URL, we can open it with run-mailcap
-    if which run-mailcap >/dev/null &&
-       (echo "$1" | grep -q '^file:///' ||
-           ! echo "$1" | egrep -q '^[a-zA-Z+\.\-]+:'); then
-
-       local file
-       file="$1"
-
-       # Decode URLs
-       if echo "$file" | grep -q '^file:///'; then
-           file=${file#file://}
-           file=$(echo "$file" | perl -pe 's/%(..)/pack("c", hex($1))/eg')
-       fi
-
-       run-mailcap --action=view "$file"
-
-       if [ $? -eq 0 ]; then
-           exit_success
-       else
-           exit_failure_operation_failed
-       fi
+    # Paths or file:// URLs
+    if (echo "$1" | grep -q '^file://' ||
+        ! echo "$1" | egrep -q '^[a-zA-Z+\.\-]+:'); then
+
+        local file="$1"
+
+        # Decode URLs
+        if echo "$file" | grep -q '^file:///'; then
+            file=${file#file://}
+            file=$(echo "$file" | perl -pe 's/%(..)/pack("c", hex($1))/eg')
+        fi
+
+        check_input_file "$file"
+
+        open_generic_xdg_mime "$file"
+
+        if [ -f /etc/debian_version ] &&
+            which run-mailcap 2>/dev/null 1>&2; then
+            run-mailcap --action=view "$file"
+            if [ $? -eq 0 ]; then
+                exit_success
+            fi
+        fi
+
+        if mimeopen -v 2>/dev/null 1>&2; then
+            mimeopen -n "$file"
+            if [ $? -eq 0 ]; then
+                exit_success
+            fi
+        fi
     fi

     sensible-browser "$1"
-
     if [ $? -eq 0 ]; then
         exit_success
-    else
-        exit_failure_operation_failed
     fi
+
+    exit_failure_operation_impossible "no method available for opening '$1'"
 }

 [ x"$1" != x"" ] || exit_failure_syntax

Please upgrade to the latest xdg-open, and I will mark it "work for me"

By the way, I copy my xdg-open to Jiajun's machine, it works.

Verified in master:a02280f99f05b1c21de2a78de9222a2f62a0dabc.