Creating a local bitmap index

Hi,
   I need to create both local bitmap indexes and local btree indexes on various large range-partitioned tables in my database and, to reduce the time taken, I create each index in parallel. I find that I can get the creation of a btree index to use more than 1 parallel slave per partition but for some reason I cannot get the creation of a bitmap index to do the same - the best I can achieve is 1 slave per partition. Am I doing something wrong, or is this merely a restriction?

   Any thoughts would be very welcome.

Thanks and regards,  Andrew.