Such a thing is almost
always a map issue. Speed limits come from the map files. Not Primo, not satellites, etc.
There was a particular release of Teleatlas maps that were particularly bad at this in certain regions.
If you are using Teleatlas, try a Navteq map for the same area, if possible, and see if the results are the same. And vice-versa.
PS. If it is Europe maps that you use, the latest are here (if you are using older releases, a newer release may also solve your problem):
Europe Teleatlas MapsEurope Navteq Maps