Currently, if the display configured for a panel is not connected, the panel just does not appear. In some cases it would be desirable that the panel defaulted to a different output/display. This is my use case, if it's worth mentioning: I use a laptop with a second, eternal LCD display. When connected, I use this display as primary and set the menu, taskbar, etc. to show there (using a external keyboard/mouse to be in front of this display). So I would set my panels to show on this, "second" display of X. But when using the laptop alone, I would want (need!) that those panels appear in the current and only output. I asked about this originally at xfce forums: http://forum.xfce.org/viewtopic.php?pid=20793
We are seeing this in fedora as well: https://bugzilla.redhat.com/show_bug.cgi?id=677645
From the downstream bug: "With the latest update (4.8.3-1) works a bit better - if I choose output: Automatic, it's on external monitor when it's connected and on laptop monitor when it's not connected. But if I choose Monitor 2 (external) it stays there even when xfce is started without the external monitor."
Using 4.8.6, but it's still not smart enough. When I set output to Automatic it always reverts back to the laptop screen and not to the external monitor. Would it be possible as Hernan says, to remember the user setting (e.g. CRT1) but to temporarily switch back to the other monitor when the external is not connected? Now the panel is just gone when the eternal is not connected.
I agree with Joost. This still doesn't work well with a notebook setup.
Unfortunately this still happens. If I set the panel to show on an external display (in the settings dialog), and then disconnect the display, e.g. by disconnecting the cable) the panel is gone. After re-connecting the display the panel will re-appear on the external display. IMO the panel should get visible on the laptop display (or in general on one of the remaining displays) if the display disappears where the panel was set to before.
We meanwhile have introduced the "primary" option in the panel's output setting, so you can better control where a panel will show up. Plus it should fall back to the internal laptop monitor if you disable external outputs (even more so if you configured a display profile).