my rebellious lower panel

Another recurring bug: Now, icons, applets, etc., move around, even after I lock the lower panel on the screen, even after rebooting, even after I have gone through several sessions and reboots. Sometimes icons and applets appear on top of one another, or disappear altogether. I unlock the panel and drag everything back to where I want it, lock it again, then everything seems to settle down for a session. And when I reboot, it's all messed-up again. Everything was fine for months on end, until I made the mistake of trying to nudge some icons slightly to create a little more empty space. (I even restored them to their previous state, and relocked the panel, but that didn't work.) I've enclosed some screenshots as attachments, so that everybody can see how I want it to look (right) and how it gets messed-up (wrong). Note that there are several marked "wrong"; and that these kept moving round even though I had the panel locked at the time. By the way, I am running Debian Jessie 8.8.0 (upgraded to 8.10 or whatever), and Trinity R14.0.4. Any suggestions or observations will be appreciated. Thanks! Bill