Alot of the time, when I'm browsing on my iPhone (which is ALOT) the login process is quite odd.
Sometimes it keeps me logged in. Othertimes I have to log in several times, when switching forums it logs me out or even switching threads. It has even logged me out after hitting submit after I've typed a reply. It can be a major hassle and I've lost some good comments. Sometimes I just give up.
It's like the "keep me logged on" box doesn't work at all too.