Issue When Editing WordPress Posts on Mac

I have noticed something recently (it may be a WordPress problem, it may be a Mac Safari problem):

When publishing/saving a post on my blog using Safari on my Mac, it removes the paragraph separations. Everything looks fine while I’m editing the post, but when I look at the post in the blog all the text just runs together.

When returning to edit the post, the paragraphs continue to be missing.

If I go into edit the posts, or creat a new post on my Windows XP box using IE7, the paragraphs work properly.