I've just noticed that the game doesn't manage to start anymore. After reading the logs for some time, I think I figured out where the problem is coming from. On Gentoo, in order to support multiple installations of the JDK, there is a symbolic link system managed by another program (/usr/libexec/eselect-java/run-java-tool.bash). This program cannot be called directly to force users to use symbolic links like /usr/bin/java. I guess the problem is that instead of calling /usr/bin/java directly the launcher tries to execute the target pointed to by the link: for this reason, it fails (as you can read on lines 131 and 132).