There's a FAQ entry which says drafts can be accessed via the User Control Panel:
This didn't work for me. Neither with a draft for a new topic, nor with a draft for a new reply. To find my drafts again, I had to create a new topic or reply. Then, in the empty form for the new post, there's a "Load draft" button next to the "Save draft" button.What is the “Save” button for in topic posting?
app.php/help/faq?sid=79d6de419a7d769c59 ... acc0#f2r10
It seems the button has also been renamed from "Save" to "Save draft" since that FAQ entry was written.