Actually, the behavior comes from ne global css, which is loaded with the RadEditor. You can stop it from being loaded in the cotent area of the content block (since it removes the spaces). This is done by setting the EditorCssFile to an empty css file. In order to do that go to Administration -> Settings -> Advanced -> Appearance and set the RadEditor content css to the relative path to an empty css file (one that you've added to your project). This will prevent the default styles from being applied. Please take a look at the image for further reference.
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