[frs-22] After killing a thread or request, or after FusionReactor CrashProtection aborts a request, I receive java.lang.IllegalStateException, javax.servlet.ServletException and java.lang.ThreadDeath error in the standard error log.

This behaviour is expected. The initial ThreaDeath error is actually caused by FusionReactor when it terminates a thread or request. The subsequent IllegalStateException and ServletException errors are thrown by JRun when it detects that the underlying thread has been killed, tries to warn the user and find that it no longer has access to the output stream for that request. FusionReactor doesn't try to filter out any exceptions so they work their way up the stack as expected and are output to the standard error log.