I haven’t been able to re-create this in my designer. Is it possible for you to make a short video of what is happening? The copying might be bringing in over hidden characters that is causing strange behavior.
I find that happening when I copy and past text from a word doc or email.
I want to point out to you that if you want to have separate paragraphs you need to use a separate paragraph element for each one. Hitting enter within a paragraph element doesn’t create a new paragraph it adds a line break to the html.
Dealing with multiple paragraphs should be come easier in the future with the addition of rich text nodes. You can read about them in this post.