Maybe I have the answer...
The car is "jumping" on the map when there is no data or data issue !
I made this video this morning (sorry for the poor quality).
My speed is quite constant.
We can see that there is no data (Waze is in red on top of the screen).
After going to airplane mode and reverting back to standard mode, no more data issue with Waze.
This phenomena can explain why sometimes the car is "jumping" on the map - Maybe the data rate is not enought for client.http://youtu.be/WByzHY__P30