forced to save before preview!?

I have been using DW MX on Win XP for a while & recently purchased a 17"
PowerBook. I'm running DW MX 2004 on the Mac & before I can preview a page
(F12) I'm forced to save the work...

?!

This means if something is haywire in the preview, I can't revert to the
previous version - rendering the "preview" feature all but useless ... what's
it "previewing". You're forced to finalized your work before you can test it in
the browser.

This is only true of the Mac verison - this isn't the case on the PC.