If a line inside of a code block is really really long and you have the split mode on, then on the preview panel you see the border for that code block to have a width limited to the panels width instead of following that really long line; thus when you scroll, you see the remaining line out of the borders of the block.
If a line inside of a code block is really really long and you have the split mode on, then on the preview panel you see the border for that code block to have a width limited to the panels width instead of following that really long line; thus when you scroll, you see the remaining line out of the borders of the block.