Postings not "taking"?
 

I have had a few problems with making a reply with no posting?

It's often a problem with your cache - i.e. your browser or proxy caches the old page and displays that version rather than the ammended version with your new post. Try clearing the cache on your computer. Also try re-downloading the page from the source rtaher than any cache (Shift-refresh for Netscape and IE, I think).

Why does this happen only some (a minor amount) of the time?

It seems it takes looooong time (sometimes more than a minute) for a reply to be added (or shown up) under a topic with many replies like 7 pages long, after it has been submitted.

This might be the cause of not being able to see your new posting, and eventually attempting to do multiple posts because you can't see it.