I would appreciate it if the site would not log me out after I have logged in and trying to post something.

E-mail "support".

It's been doing it all morning, It's not just you.

It's the internet, it operates on the S.I.U.A.S.C protocol:

Suck It Up And Stop Complaining .

I thought is was the F.U.B.A.R. principle.

Might also be your browser settings. Something might have triggered a change in cookie handling and site preference settings.
I had a similar problem with sites since I got this new computer and come to find out it was in my browser settings. I tweaked them and the problem went away.

If you are using an app, try using a browser app instead.
Look at refresh rates and what happens during a refresh.

it's happening to me now too. yesterday it was still ok

Mingle does that to me as well. Not like every week but it does happen every now and then. Really annoying, but yeah...