As promised, here's the patch in bugzilla, along with the announcement Email

So, why did I have to write this patch?                                         
                                                                                
1) I use MAPS DUL and relays.osirusoft.com, which also has a DUL section.       
   The problem is that I had machines that were being penalized twice for       
   being on more than one DUL.                                                  
   This actually let to some non SPAM being reported as spam more than once     
   (and my threshold is 7, not even 5)                                          
                                                                                
2) Furthermore, we shouldn't overly penalize people because they're sending     
   mail from a dialup IP if they properly relayed through their ISP             
                                                                                
3) There was no support for querying multi RBL zones like relays.osirusoft.com  
   Let's say  an IP  is flagged  with a  score of  2.0 as  an open  relay in    
   orbs. Because there  is already a  match for set relay,  osirusoft checks    
   won't run against it, even if you had a match (2.0) plus a return code of    
   # 127.0.0.6 which would have given you another 3.0, so you lose a perfect    
   5.0 score.                                                                   
                                                                                
4) Probably a few other problems of that sort                                   
                                                                                
                                                                                
Over the  last 7-10  days, I tried  different ways to  fix this,  some being    
rather misguided,  trying not  to run  tests if other  ones ran,  and having    
overrides to  ignore the  first IP  for dul, which  gets interesting  if you    
compare checks  in set  dialup and checks  in set relay  which can  return a    
match of dialup.                                                                
Needless to say, this went nowhere, I couldn't understand my own code before    
long.                                                                           
                                                                                
The next idea, to change the score of some rules to 0 if other ones already     
matched seemed misguided too, especially since I wasn't sure if it wouldn't     
cause problems with spamd                                                       
                                                                                
I eventually came up with this: adding rules to counter other ones, and         
using a function called check_two_rbl_results to add a negative score if        
two RBLs matched on the same thing.                                             
Putting osirusoft in set relay was also a mistake, I've put it in its own       
osirusoft set since it can have many different meanings.                        
Last, but not least, an RBL rule  that ends with -firsthop is magic, it only    
matches on the originating IP provided there is a relay in the middle           
                                                                                
The rest should make sense if you look at the diff and the example RBL rules    
in the docs