That may explain it, I don't use Safari very often so it may have something to do with Safari and/or OS X's equivalent/implementation of WebView.
I remember a while ago having cursor issues with Flash being loaded on the page where it would disappear and I'd have to switch windows or something to get it back. You might want to see if temporarily disabling Flash improves the issue for you (or set it as click-to-load).
Edit: Woo Office update, that (hopefully) fixes my cursor issues at least.
Image
As an aside, I should mention that I had a Java based chat room running at the time, perhaps that's relevant. Typically navigating away from the window where the cursor is invisible to the desktop itself restores it and it will behave normally after the incident. The cursor, though invisible, is still hot. I can see where it activates hot links, just not the cursor itself.