I cleansed my system of the 255 binaries and all the 254+ associated structure and import files when I reverted to 253 as I needed a working system.
From what I can tell, I can't run 253 in parallel with 255 or 256 for that matter in order to to repro the scenario and yet keep a working environment for my system without having to cleanse the master db and resync back from the server.
The issue I kept hitting which prevented upgrading past 253 however is very succinctly explained by Acenoid here:
http://forums.wolflair.com/showpost....36&postcount=7