When pasting in the content block the text will be presented as copied. If you have copied and HTML text which includes <a> <div> <h1> they will be added to the content block as they are.
For a possible solution to your problem expand more formatting options and use the stripper tool to strip the formatting that is problematic. If this does not help please provide me an example of copied text that will demonstrate the problem or where should I copy from to reproduce the problem. Currently copying while e-mails puts the past line in <p> and closes it.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items