There's an Openbox dev with a special "work" branch separate from normal upstream Openbox (I believe). He's got quite a few changes in there, I wonder if any of them affect this. I might try throwing a Git build of that into a PPA and asking for testing, if it works we can git bisect and figure out what fixes the problem, then patch things in Lubuntu and forward the patch to Debian.
There's an Openbox dev with a special "work" branch separate from normal upstream Openbox (I believe). He's got quite a few changes in there, I wonder if any of them affect this. I might try throwing a Git build of that into a PPA and asking for testing, if it works we can git bisect and figure out what fixes the problem, then patch things in Lubuntu and forward the patch to Debian.