Interpreter scoping, possible bug

Hi,
  I have a situation where I want to compartmentalize each script I
evaluate in an interpreter. Right now, I'm using a separate interpreter
for each script. Is there a significant cost to doing this? The reason
is that I set some variables on the interpreter that are unique to each
script and I don't want any co-mingling of these variables or access.

  What is the basic overhead cost of an interpreter? e.g. threads.

Also, I have noticed a peculiar thing. In a callback method from my
application to a 'class' instantiated in beanshell and exposed to the
Java app, some variables will not access properly WITHOUT a class
declaration. The script just halts when you try to access, without a
runtime exception. I'm using the latest beta jar of BSH and JDK1.5_01.

Thank you!
Darren