Minor nit, but this should really by CURRENT_GROUP to stay in line with java naming guidelines. 

I'm also not really sure I like a thread local stuck onto an interface, but I suppose it makes sense in this case. 

I think there may be some scenarios where this thread local approach can cause problems, however I am not sure if they are such edge cases that they are not worth worrying about. In particular say you have a SFSB that makes an invocation on a SLSB that then creates a SFSB. Conceptually the second SFSB belongs to the SLSB, however it will be included in the original SFSB's group. 

Like I said though, I am not sure if this is really worth worrying about.