Andy- I'm amazed that you've seen BLM rangers handing them out! I guess a stretch like Pumphouse where most people do it as a day run might have been having problems with human waste at lunch spots. I think our combined experiences show how disconnected not only all the different agencies are, but also how much it comes down to ranger judgement and mood as to what he's going to allow from one day to the next.
This goes for people on the phone, as well. If you have a question about whether a piece of gear is going to pass muster, don't rely on the girl who's worked in the river office for 3 months to tell you what's going to be allowed- ask to talk to, or better yet, e-mail (so it's in writing) the head river ranger.