Oh well if its lead-in then its obvious. The program area of most records is almost perfectly flat but the lead-in area on some records is curved with a bit of a lip. So its possible depending on the angle and your anti-skate for the stylus to touch down in the flat area between the grooves, then "ride the curve" downhill at about the same rate as the lead-in groove, so instead of falling in right away its going along the flat surface a turn or three.
The only other explanations are dust or a sticky arm. I find it hard to believe slaw has a problem with either of those. He's too good. So it has to be the lead-in lip. I've had the same happen to me, just hardly ever, and I know what it is so no big when it happens.
