Cobertura is configured with an unstable threshold. The build is successful but
the plugin sets this build to unstable. In this case, we don't receive a mail
saying the build is unstable.
At the next build, if this one is still successful but unstable, we receive a
mail telling "the build is back to stable"… but it is not true. In fact the
email is sending before the build is setting to unstable.

Maven2 project configure as free-style project on Hudson 1.183 with Cobertura 0.8.4.

(Same issue was noticed with the Clover plugin (1.6) and Hudson 1.183.)