You mention the pen. Aren't you using the Wacom mouse? You need to hold down the right and left mouse buttons at the same time to move the tune. If that doesn't work, then there may yet be another issue going on.
No, I have the Intuos One. Always worked like a charme. Never felt, I needed another one. Given my observations I think now it's a bug. And since the Wacom drivers don't change much it is quite likely an iTunes bug, incompabitibility coming with the last update or something..
When you have the playlist displayed in iTunes, the column header above the track numbers has an arrow (chevron). Click on it and it toggles the order of the songs. This is what enabled me to move songs to different places.