I confirmed that on Ubuntu 12.04 lxpanel 0.5.8+git20120212-0ubuntu3 and disabled volume control item run command window apears only ones. If volume control panel item is enabled, run command window doesn't appear by alt-f2 and "lxpanelctl run" doesn't work too. Also enabled volume control item leads on graphic artefacts on lx panel.
I confirmed that on Ubuntu 12.04 lxpanel 0.5.8+git201202 12-0ubuntu3 and disabled volume control item run command window apears only ones. If volume control panel item is enabled, run command window doesn't appear by alt-f2 and "lxpanelctl run" doesn't work too. Also enabled volume control item leads on graphic artefacts on lx panel.