Are lxpanel launcher icons supposed to vary by desktop environment?

I have custom lxpanels in Lubuntu 16.04, designed to mimic appearance of Unity. This works wonderfully in Lubuntu/LXDE session...Unity without the bloat!

However, I've been using Fluxbox and Openbox more frequently. I have noticed that lxpanel launcher icons are slightly different when started with "lxpanel -p [custom layout]" in Openbox or Fluxbox environment, as opposed to default Lubuntu/LXDE environment. Openbox and Fluxbox both display lxpanels identically, but not the same as LXDE; which is even more confusing when you consider that Openbox is the window manager for LXDE. I can modify the panels from within Fluxbox/Openbox, but then LXDE displays them differently. This would seem to suggest that LXDE is doing something different to display lxpanels. Or is this a bug?

I'd like to switch back and forth between LXDE, OpenBox and Fluxbox sessions without reconfiguring lxpanels between sessions. How can I get lxpanel to display correctly in Fluxbox/Openbox session?

I am using Lubuntu 16.04 defaults, with default Fluxbox. No fancy builds from source, just stock offerings from Ubuntu/Lubuntu. Anyone else experiencing this issue? Please advise. Thanks in advance for any insight offered!

**EDIT**: After much troubleshooting & tracing, I have concluded that lxpanel is working fine. It appears that lxpanel is displaying icon/launchers in the panel in accordance with config files for lxpanel. And when an icon is missing, it is because of a null path in menu://applications bookmark of PCManFM. For some reason, PCManFM displays the applications in the menu://applications bookmark differently, depending on the desktop environment. This appears to be an issue with PCManFM displaying applications differently between an LXDE/Lubuntu environment, and a naked window manager environment. As long as you stay within one environment, everything is fine. Switching back & forth between the two causes these issues. FWIW.