NullPointerException when I have multiple python udfs

When I have multiple python udfs registered, the script fails at compile phase while trying to get the udf ouputschema.

register 'a.py' using org.apache.pig.scripting.jython.JythonScriptEngine as a_func;
register 'b.py' using org.apache.pig.scripting.jython.JythonScriptEngine as b_func;
a = load 'i1' as (f1:chararray);
b = foreach a generate a_func.helloworld(), b_func.square(3);
dump b;

a.py

@outputSchema("word:chararray")
def helloworld():  
  return 'Hello, World'

b.py

@outputSchemaFunction("squareSchema")
def square(num):
  return ((num)*(num))

Moreover , in the log we can see duplicate and incorrect registration of udfs which I believe the cause for the script failure.
INFO org.apache.pig.scripting.jython.JythonScriptEngine - Register scripting UDF: a_func.helloworld
INFO org.apache.pig.scripting.jython.JythonScriptEngine - Register scripting UDF: b_func.square
INFO org.apache.pig.scripting.jython.JythonScriptEngine - Register scripting UDF: b_func.helloworld

This issue is observed in 0.9,0.8 and in trunk also.