Using PageUp or PageDown does not move the current cursor location (it should). Try using PageDown twice then LineDown once. The displayed text jumps back to where the cursor now is; one line down from its position prior to the two PageDown steps. The cursor should be someplace in the region of text displayed by the second PageDown.

Well, the current behaviour is what virtually every editor (I use) uses. I can make it a preferences option though.

Fixed. New script editor setting: "Page up/down moves insertion point". Each time you use the Page Up or Page Down keys, the insertion point is moved to the first visible line.