Google employee Joel H responded to this query on 22nd April 2009 but I can't see any recent updates from Google employees.
I've just noticed the same problem with my businesses listing. Have Google's systems yet been update so business can be unmerged when Google have incorrectly merged them? The various posts on different threads here seem to suggest that there are numerous cases of completely different businesses operating from the same address who are having their records merged.
In this case, our letting agency has a different phone number, URL and catogory listings from our Roller shutter installation business. Our two seperate business center accounts are fine, but searching for Roller Shutters in Nottingham brings up the letting agency. Which isn't what we want.
Surely there must be a way of fixing this by now?
If not, please can somebody within Google raise this query to see how us innocent parties can have their entries straightened out?