WordPress and Safari have issues. Well more accurately, TinyMCE and Safari have issues.
TinyMCE is the visual editor that WordPress uses and it can’t work with Safari. The most obvious way you see this is WordPress not keeping the format of your posts once you have published them, especially the paragraph breaks.
What’s the answer? Use Firefox or Opera. It’s a crap answer. Safari 3 was getting real nice. Stable and quick.