In the extra material for the season 1&2 disc, Cybill says that they sometimes had the script in front of them when they did the car-shots. Here I think I can see proof of that!
Right before Maddie get David thrown out of the car (after the word boink is frequently used) you can see some pieces of paper before him.. And I can´t remember him bringing any other paper into the car. He´s not a note-taking kind of guy. Keeps it all locked up in his mind.. Watch it and see for yourself.
No problem. ;D Given what she said about keeping script pages in the car just in case, though, I wouldn't put it past them to have at some point let stay some little continuity mistake in a different 'driving around' scene, perhaps. There are plenty of other examples of them being in the car, so who knows, maybe we will catch one. ;D