I have been wrestling with this problem (or similar) for about the last two weeks:
Basically, this is caused by:
1. VPE spinning a build which includes org.jboss.tools.xulrunner.initializer 3.1.0.v20110726-1048-H409-M3, then
2. JSF (richfaces) spins and picks up that H409 build and includes it in its site. Then,
3. while the JBDS update site is spinning,
4. the VPE build spins again and now depends on H410 instead of H409.
5. Because the aggregate can only include ONE version and each feature has strict plugin version requirements, there is no solution for p2 to be able to create a site with the two versions of the plugins installed concurrently.
So, either we need to build these two components together as a single job, or we need some other way to ensure this "vpe respin breaks jsf installability" problem is solved.
Maybe the richfaces.feature should DEPEND ON the xulrunner.feature instead of INCLUDING the org.jboss.tools.xulrunner.initializer plugin? Or just depend on that single plugin (again, rather than including it) ?