I have a 06 Laguna Initial.
This will fix it for a while at least. Go to the menu and choose Navigation. Then scroll down and choose adjust your current location. Then zoom out/in as required and move the cursor to where you are right now. Press select then rotate the knob until you are pointing in the correct direction along the road you are on now. Press select and it has reset. The more acurate you are, the longer it will last.
Why this happens, I don't know. But this fixes it temporarily. I reset every day or so.
chris H
August 2011