Its not a bug because the problem is due to your development environment.
Unfortunately I haven't a clue what is causing your error however I do know that alfresco compiles fine for me on the Sun SDK. I think your first port of call would be to make sure you have a Sun JDK; from memory there was a problem with some of the other java 6 JVMs which were missing Rhino which is why alfresco 3.3 had a fairly specific set of JDK/JREs to run on.