For some reason I need Xlibs_support to boot into jwm, or it loads flwm with lots of extensions not loaded.
Add back Xlibs_support, and eveything boots up correctly.
Without Xlibs, I can load eveything once in X (including jwmwm), no problem.
(it's not libXss or libXv)
Edit: ah......it's listed as a jwm-snapshot dep; maybe should be listed for jwm.tcz as well
note: It's not needed if you load a group that includes jwm from base option.