My phone is Android and I run a lot of hotspots, so I have used MT hotspot quite a bit with Android.
My experience is that when the browser is first launched, Android pretends it is loading a page when it isn't - it is taking it from cache - especially if
http://www.google.com is the homepage.
If you wait for it to pretend loading and then refresh the page or hit a bookmark, the page actually loads, which triggers the hotspot intercept.
Try that, if that still does not work, post the hotspot page html.