New posts not showing themselves

Sounds weird. Did you notice the time the post was submitted relative to the time you clicked the thread? Maybe it just appeared the second you clicked the link?

Could also be a cache issue - if your browser is caching the index pages, say, then they might not get updated as frequently as they should.

I use Opera and I can't recall experiencing this problem. If it happens again, try to capture the time you clicked, the time the "new" post was submitted and let me know here.