EXECUTE: Create several CDI and/or Seam and/or JSF projects.
EXECUTE: Select them all and run Clean/Build.
EXECUTE: Wait for a couple of seconds for a progress to show the build on its way, and invoke 'Close Project' on the entire selection.
EXECUTE: After a couple of seconds invoke 'Open Project'; this two steps may be repeated until the log is full enough of the catch.

Discussion is started in JBIDE-10111.
The exception is caught and logged. It is not easy to check everywhere for accessibility, and even

if(project.isAccessible()) {
    project.findMarkers();
}

may fail if project will become inaccessible right between these two calls.
Maybe we should try locking a resource while it is validated, but that should not hang workspace for the entire build.