Well, if you were really waiting in the car at a gas station (and not driving like a maniac ), then there probably is no explanation other than simple GPS inaccuracy. It does seem strange that there might not be anything interfering with the GPS signals that you're receiving, but Maemo Mapper doesn't do any translation or modification of the data that it gets from your GPS receiver - what you see is what Maemo Mapper got. So, it's probably just a momentary signal lapse.

For what it's worth, Maemo Mapper does try to "ignore" GPS data that is "sufficiently close" to previous data, based somewhat on the "dilution of precision" (roughly correlated with the estimated error) of the GPS fix. But the effectiveness of that varies quite wildly from GPS receiver to GPS receiver, depending on how well a particular one measures DOP. And the code tends to err on the side of safety, so in many cases, it will plot data that a human would probably throw out.