PREFACE: I have not read all the posts in this thread, merely the starting post and scanned a couple others.
That being said, it sounds like caching.
You may all be familiar with how a web browser caches copies of websites on your local computer (the idea being that it can load static content pages quickly since it only has to pull it off the local machine rather than download every single time you visit said website). The common fix is to simply to and clear out your cache.
One thing that is emerging the ISP industry is caching software on some of the ISP routers. It isn't mainstream or widespread, but some places do use it since it cuts down on costs (your computer pulls pages from a cache copy kept on the router rather than needing to go across the internet to retrive everything).
The fix?
If it is being saved as cache on your local computer, empty out your computer's cache.
As an add-on, if you use a windows machine, hold down the Shift key while you click the reload button. For macs, I believe it is the control key you need to hold down while clicking the reload button.
If we are talking about a cache copy on a your ISP's router, then, unfortunetly it is not as simply as the above two. That first requires a conversation with your ISP (or system admin, or whomever) and ask if the router (or something) stores cache copies. If you can confirm that it does, keep the conversation going with the system admin/isp to see if you can request excemption domains to the caching (or perhaps ask them if the frequency that the router's cache gets cleared can be made more frequent). If they say they do not have caching on the router (or whatever) -- and you know you are talking to someone knowledge enough to actually know the _real_ answer to the question -- then your difficulty can most assuredly be put back to your local computer. Some software setting or adjustment on there ...
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Anyway, this may or may not be the problem at hand, but just offering it as yet another possibility (/possibilities).
PS. My point summarized without my usual ramblings: If it has all the same symptoms of your computer caching but you've already cleared the cache (and you've also already tried the hold down the key and press reload trick) then it could be that your ISP is caching at the router.
Edit: Adding the PS since everything else I said comes off as a ramble
