Generics compiler bug?

I've been using generics for a few years, and I'm happy with them. I'm
aware of the issues related to their design, and I agree that they
could have been made a bit better (but I understand the trade-offs made
for backward compability), but on the whole I consider them quite
useful for writing better code. I haven't had any problems so far, but
now I got stuck with a thing that looks like a compiler error. Consider
this class that I'm using as a transactional decorator (*) in my
NetBeans RCP stuff:



package it.tidalwave.bluemarine.persistence;



...



public abstract class TxTask<T, E extends Throwable>

  {

    ...



    public abstract T run()

      throws E;

   

    public static <T> T
execute (final TxTask<T, RuntimeException> task)

      {

       
return execute(RuntimeException.class, task);

      }

   

    public static <T, E extends
Throwable> T execute (final Class<E>
exceptionClass,

                                                     
final TxTask<T, E> task)

      throws E

      {

           
try

             
{

               
...

               
try

                 
{

                   
result = task.run();

                   
...

                 
}

               
catch (RetryException e)

                 
{

                   
...

                 
}

               
catch (PersistenceException e)

                 
{

                   
...

                 
}

             
}

           
catch (Throwable t)

             
{

               
...



               
if (exceptionClass.isAssignableFrom(t.getClass()))

                 
{

////////////////////// THE PROBLEM IS HERE

                   
throw (E)t;

////////////////////// THE PROBLEM IS HERE

                 
} 

               
throw (t instanceof RuntimeException) ? (RuntimeException)t : new
RuntimeException(t);

             
}



           
...

         
}

       

       
...

           


       
return result;

      }

  }



The peculiarity of this class is that it uses a generic in
the "throws" clause. This is ok with the language specifications, see
for instance the excellent href="http://www.angelikalanger.com/GenericsFAQ/FAQSections/TechnicalDetails.html#Can%20I%20use%20a%20type%20parameter%20in%20in%20a%20throws%20clause">Angelika
Langer's tutorial on generics (even
though it's considered pretty useless in most cases, since you can't
throw a generified exception because of type erasure - but in my code
things are ok since I'm just rethrowing).



Now, the history of this issue is pretty complicated:

1. The thing worked for several weeks, if not months (I remind
   you, in a NetBeans RCP project)
2. At a certain point, I copied the class in the prototype of
   a
   web application, and I got a compiler error (see below); since I was
   focused on other things, I just commented out the offending part.
   blueMarine was still compiling ok.
3. Since a few weeks, this is triggering the compiler error
   even in the NetBeans RCP project: but ONLY IF I BUILD THE WHOLE
   PROJECT (that is, if multiple *.java files are compiled at the same
   time). If I select the single TxTask.java file and compile it with
   the pop-up menu, it gets compiled ok (in fact, with this trick
   blueMarine builds, runs and passes the tests).