I found out what's the problem. I experimented running JBoss AS 7 with jdk7 through JBDS in 2 platforms, Mac OS X and Linux, and both presented the issue described previously by me. When running in the same way on Windows Seven (with Oracle JDK7) everything worked fine.
So I guess the issue is between JBoss Tools and openjdk7.
By now I'm returning to openjdk6.