Comment 4 for bug 1993186

Ah, so you didn't restart the panel? I can observe the same behavior (4.17.4).

My guess is that the old configuration is still in memory, so adding new plug-ins "revives" it. If I monitor the whole channel:

`xfconf-query -c xfce4-panel -mv`

I can see that when I add a new plug-in it appears as:

set: /panels/panel-0/plugin-ids ((null))

and isn't retained after panel restart. What's more interesting is that the default plug-ins are also loaded in the process but the whole panel-0 is inaccessible and unusable: probably because position and size properties weren't set (or wiped during reset).

Resetting both /panels and /plugins, then restarting the panel fixes it. Panel IDs are stored in arrays and start from 1.

To conclude, xfce4-panel (at least the latest version) seems to prefer one-indexing newly added panels but won't refuse older configurations if they're loaded at once.