Nope, I wasn't doing anything special - just opening nodes 4 levels deep in the tree or for some reason publishing seemed to trigger it too. I thought this was a bug in the odcsm extension, but I deactivated this and the bug recurred in the standard non-ajax csm. I filed a bug report last night, since this particular site isn't big (only 360 nodes so far) and this didn't occur before I last upgraded (running from the 3.8 stable series svn).
http://issues.ez.no/IssueView.php?Id=9319
...I'm not sure where the bug might be though, and I don't have time to dig deeper. (Anyway, I did my share of volunteer late night critical ez-bug hunting already this year ;-)
For now I increased memory_limit to 128M which has "fixed" it, although to be honest I'd rather lower it again. No web page in its right mind should really need more than 64M of RAM to load.
