Hi Marko,
mkgmap does not like this relation: http://www.openstreetmap.org/browse/relation/55796
except = destination;taxi restriction = only_straight_on type = restriction
It does not recognize the 'destination'. I thought that I would ask if mkgmap could support the analogy of access=destination on turn restrictions.
In this case, I think that the proper fix is tagging the forbidden destination street (Keskuskatu) entirely as motor_vehicle=destination. It is a narrow street crowded by pedestrians and construction sites, and the other end of the street (Aleksanterinkatu) is flagged motor_vehicle=destination, maxspeed=20 by traffic signs.
Once again, this is something we don't know about. There is a whole lot more to turn restrictions than what we understand at this time. For example, turn restrictions can have on/off times/days. Also, I believe you can have more nodes involved in the restriction than we currently support (perhaps, one day that will provide a solution to the via "way" problem). Cheers, Mark