Are you using RS-485 4 -wire (Nodes transmit on 1 pair, receive on the other)?
Yes I spent over a year on and off working on a multi-drop/master-slave protocol then finally dropped it in favour of a redundant-ring/peer-to-peer, so I've had to totally rewrite the design.
In the process I've also slashed maybe 80% of the complexity, I want it to be reliable and have no DIP switches to set addresses etc so it's inevitable that some complexities will occur. But I think it will be fairly simple.
I have a finished schematic for a prototyping board and have started the PCB layout.
The design currently uses a Mega1284 at each node, it's not ready for public consumption yet but I'll email you (and anyone with a real interest) a document.