YES! I noticed that too, if I come back after a while this happens. But what I noticed is that instead of "logging in", just click on the cubebrush logo to go to the "homepage" and you'll be magically signed in. It's like the browser saves your session but forgets to display you are signed in until you navigate around. So when you try to "login again", it doesn't really log you in since you already are logged in.
It's weird, I just kinda got used to it. Doesn't seem to happen on my cellphone.
Seems to be similar to point one and related to your active session. If you do something lke set forum threads to your browser favorites and then go directly to that link, this seems to happen, but if you just navigate around, it works fine.