Copy pasting text into the new editor causes the page to "jump" to the end of the pasted text rather than staying put

Steps to Reproduce:

1. Create a page with a lot of content to the point that there is a scroll bar on the right side of the textarea:
   
2. Copy and paste some text into the editor, and notice that the scroll bar jumps a bit, and scrolls to the end of the pasted text

Copy and pasting in Confluence 3.5 does not create such behavior, rather, the scroll bar stays put without moving. The new behavior annoys some users, as it is hard to keep track with the page movement, especially when there is a lot of content in the page.