Creating multiple instances of the subreport was precisely what I was thinking about. Unfortunately I don't have a usable solution right now, just some ideas of paths that need to be explored.

As for why you can open multiple instances of the report that uses "rptbsub", the first thing that comes to my mind is that "rptBsub" does not iterate through a dataset in order to print one row at a time, but performs some kind of global data processing prior to produce any graphic object.

Once more these ideas are just speculations and I need to test and (in)validate the hypothesis.