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.
I discussed the problem with Safari with my colleagues from the RadControls team and they are not aware of such problems in this browser version. I also tested this behavior by opening the RadEditor demo page in Safari (this didn' cause any malfunction). You can take a look at this thread, where a similar issue has been discussed:
As for setting the EditorCssFile, take a look at the radEditor documentation and here are two ways you can set a file through the code-behind of the editor:
// second approach