This is just another of the many and unusual buggy problems that plague the smart. The factory has to get grip on these electronic problems and deal with them using the safety recall system. Some of these issues are safety problems.
At the very least there should be Technical Service Bulletins (TSB's) supplied to dealerships that outline the problems and solutions.
The only TSB's I found for my 2008 car are listed here -
TSB Results : ODI - Office of Defects Investigation
There were none listed for the 2009 model year.
Perhaps there are others that the dealer has but it seems to me that those working on the car are at a loss as to what some of the problems are and how to deal with them. If they occur once that is bad enough, but if they continue to happen in the same vehicles then there is a serious problem.
There is also a Lemon Law. Has anyone taken advantage of it?
The ABS system has stopped working several times with my car. The only common element may have been that it was raining at the time. Each time it happened it cleared itself after a short time or after several days had passed. When the ABS stopped working so did the hillhold feature.