In the master page spread, the black bar is actually two bars (one on each page), right? Does the block on the right page touch the left page, or visa versa?
What version of ID are you using? Have you installed the latest patches?
The black bar is two seperate bars. Neither go across to the other page (using the snap feature to go to the inside fold). Oddly, when I reorder the pages, the black bars and others are extended across... all being one long bar across the double spread.
Peter, I'm running CS5, since your post I have updated to the most recent patch and there still seems to be an issue. I will try setting up a new document from scratch to see if that has any effect at all.
It seems to be an issue when Master page B is linked to Master Page A (doing this for the footer and page number). When disconnecting the two and having the same content on each master page there does not seem to be an issue. Unforunately this isn't the easiest fix cause if later the client doesn't like how the fotter looks I'd love the ability to just change one master page (that's the whole point isn't it?!). Still looking for a fix!
Try overriding the black bars from Master A on Master B so they would be editable if you wanted to work withthem on the master. I'm not saying you should move or change them, just override them onto Master B.