Well i use the website daily also, but do not post that much. But I've never faced that problem of loggin out.
The logout idle time is 20 minutes, if u don't click on any link for 20 minutes you will be automatically logged out. If you have the remember me option checked, then you will be automatically logged in.
& yes I agree that once you login you should come back to the page from where you were asked to login but that's little longer process of programming code that needs to be done from my end.