Hi!

In the script editor, I had selected a block of code to move that happened to be below one of the built-in gray "[ section ]" lines. When clicking on the up arrow, as each line of the block passed the 'section' line that line would split from the block and now have a blank line between it and the other selected lines. Those split lines then started interleaving with the script commands above the 'section' line, with the existing lines falling into the 'blanks' between the split lines.

Please let me know if you need any more info to reproduce it...

Tom