I am still having this problem - infact, I have it right now.
I have connected both my Laptop and my iPad Mini to my HTC Sensation using the portable wifi hotspot feature to test.
The laptop is working perfectly - I am using it to post this.
The iPad Mini is behaving as if it has no internet connection. It gave up trying to load the forums after a minute or so and now says 'The server stopped responding'.
Edit: And now, as if by magic, the ipad works again. Oh wait, no, its given up again. I got about 30 seconds of browsing before it suddenly decided yet again that it wasn't going to load anything.
It HAS to be something to do with the iPad surely, or my laptop would be affected by this problem which it very definately isn't?
I have never had a single problem using Wifi tethering with my laptop but every time I try to do it with the iPad Mini it's very hit and miss and usually a hugely frustrating experience that.
I simply cannot understand what the problem could be? It is only when Tethering that the iPad does this. It works flawlessly on fixed wireless networks.