Build other projects: "Trigger even if the build is unstable" doesn't work

I have a build with maven defined in hudson which should trigger another build
by using the "Post-build Actions".
I ticked the checkbox "Build other projects" and entered the project name. I
also ticked the checkbox "Trigger even if the build is unstable".
-> Everything works fine if the first build is stable. But if the first build is
unstable the post build is not started! So the checkbox "Trigger even if the
build is unstable" has no effect.