Getting reports of captive portal splash page not functioning in some client browsers. Seems that IE/Firefox tend to work, but browsers such as google nexus tablet the chrome browser and Mozilla Firefox for Ubuntu are not functioning.
I have seen portal issues pop up from time to time. Usually this issue is with the client. The clients try and resolve a specific URL (Similar to Apple's "Success Page"). If they can't get there the device will disconnect during the portal process. The only way to resolve this is to try and spoof the page for the device so it thinks it's connected (new code on the controller). Can you try and get a wireshark trace of the process? You can use the real capture function at the ap where the client is attached. I would strongly recommend that you open a ticket with the GTAC and someone can help you gather all the info on this issue.
Here is a screen capture of a trace I got on a Samsung S4. The customer I was working with reported the device reported "No Wireless Connectivity". He thought DHCP was not working because the client failed to pull an address. The trace shows that was not the case. In Frame 388, it shows a request to a specific URL. Since the device did not get the response it was looking for it roamed or disconnected. If you try and go to that page you get "welcome. test page..."