Created attachment 8320 screenshot Xfconf editor of xfce4-panel settings If user, on a multi-head display, makes changes to panel setting value "output-name", the ability to set panel to span monitors becomes disable. From a default configuration, "output-name" is set to automatic. If the user changes away from this value, a value is set and "span-monitors" becomes disabled. Even if the "span-monitors" setting is changed in Xfconf editor or editing ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml, the value of "span-monitors" is not honored by panel. The only way to re-enable "span-monitors" setting is to open Xfconf editor, select xfce4-panel, and remove the string value next to "output-name". One fix I can think of is to have a "None" option on panel settings dialog which would write an empty value to xfce4-panel.xml. Default for "output-name" can still be "Automatic", but if the user changes the setting, selecting "None" would force clear the value, re-enable "span-monitors", and allow existing code to function as-is.
Created attachment 8321 Settings Dialog after changing output from "Automatic" to anything and then back to "Automatic". Note: Span Monitors is disabled.
Created attachment 9355 [PATCH] Fix span monitors after output-name set Attached is a patch to fix this issue. It looks for both "NULL" and "Automatic" when evaluating output-name. Tested successfully in dual monitor setup - needs further testing.
Able to apply patch and attempt to build. However, autogen stops configure due to revision of libxfce4ui-2 being to old(4.13.4 requires 4.15.1). Unable to test at this time ToZ's patching to confirm issue. Confirmation will require pushing distribution to update whole xfce4 versioning.
@ToZ: While your patch looks ok, I can't reproduce the problem. For me changing the value to "Automatic" re-enables the "Span Monitors" option correctly without the patch (panel from git master).
Created attachment 9410 visually support that original problem still persists Confirming that original reported issue is still present. Providing both panel preferences and values from Settings Editor for panel. Note that the "span-monitors" value is set but it is not being honoured by the display manager.
As soon as the "output-name" value is cleared in the Settings Editor, monitor spanning of the panel happens immediately.
Just to be sure, you're not still using version 4.13.3 of the panel (which is selected in the version dropdown)? This must be the reason why I cannot reproduce the problem :) https://git.xfce.org/xfce/xfce4-panel/commit/?id=57f439b9b30c645b9b52a233056819c3b54fcc89 So this is fixed in git master and can also be backported to 4.14.
Simon Steinbeiss referenced this bugreport in commit 3c2f9814758467397830fbb49297855a55111a4b panel: Make sure "span monitors" is conditionally sensitive (Bug #15169) https://git.xfce.org/xfce/xfce4-panel/commit?id=3c2f9814758467397830fbb49297855a55111a4b
I pushed the fix to the 4.14 maintenance branch, so it'll be included in the next point release (xfce4-panel-4.14.4). If you could test the branch, that'd be helpful. Otherwise please stick around and test 4.14.4 once it's released and if the problem still exists feel free to reopen this report.