Does Vegemite have a lot of salt in it? I'd kind of expect it, as a preservative. That stuff is supposed to have a very long shelf life.
Speaking of preservatives... I just tried non-sulfur dried apricots today. **WOW**! Holy crap, this totally changes everything. I love apricots and the glowing yellow-orange dried ones look so fantastic next to the shriveled brown roach appearance of the natural ones (no added sulfur). On a lark a picked up a pack from Trader Joe's. They really do taste differently, in a very good way. I highly recommend them.