There's a difference in the way static and dynamic rivers are generated. This wasn't a huge problem until the default template for static rivers got the killer RT feature. Now everyone wants to know how they can get that for their rivers.
The only answer until now has been "Create a static river" -- which is probably good advice anyway, if you want to share your river with others, that's really the only way to do it.
Then I thought -- sheez -- why can't I just add the RT command to the dynamic river too? Took a couple of iterations, and it works. :-)