This is a severe problem, and I am experiencing it this the upgrade from Xubuntu 13.10 to 14.04 at the start of may.

Some info
=========

I use an up-to-date Xubuntu 14.04:
$ xfwm4 --version
        This is xfwm4 version 4.11.1 (revision 2b800f4) for Xfce 4.10
        Released under the terms of the GNU General Public License.
        Compiled against GTK+-2.24.23, using GTK+-2.24.23.

        Build configuration and supported features:
        - Startup notification support:                 Yes
        - XSync support:                                Yes
        - Render support:                               Yes
        - Xrandr support:                               Yes
        - Embedded compositor:                          Yes
        - KDE systray proxy (deprecated):               No

I use a 64 bits system. Kernel is currently : 3.13.0-30-generic. I use the "radeon" video driver. lspci says :
VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cedar [Radeon HD 5000/6000/7350/8350 Series]

I have one panel configured. With a workspace switcher plugin. I usually configure two workspaces.

My problem
==========

After a few hours (it varies a lot) using my system, suddenly, all the windows are "undrawn" from my display, the clock on my panel displays an hour far back in time (several hours). So I see my panel and the desktop background.

If I switch workspace (keyboard shortcut, or clicking the workspace panel plugin), everything comes back to normal. And re-disappear at a random pace (can be quite high actually).

The only way I found to prevent this behavior is to configure only one workspace.

I am not even sure this is an Xfce problem. I wish I could help more but I really don't know what or where to look for. You guys can ask me anything, I'd do my best to help investigate this annoying problem.