It may be a problem with the cookie. If your phone isn't accepting cookies, the site can't remember you (and will even forget after a click or two on the site). The site and your phone browser can't communicating well. Try looking in the settings of your browser and be sure that you are accepting cookies.
If you still are having trouble, may I suggest if you're using a smartphone or iPod, to use Dolphin Mini or the full version for a browser. I use Dolphin Mini and I haven't gone back to using any other browser. The default one is garbage and others have too many glitches.