I didn't look at the entire depth of the issue, but from what I've seen described on the referenced forum, those options looked reasonable.
So, just in case: I am not sure how the engine for this forum is done, but if there is some process running (besides just the webserver itself), - did you restart it after changing the configurations?
Otherwise, - if it is running as an extension to the webserver (module), - did you restart the webserver daemon? Basically, - are you sure the changes you made were loaded/picked up?
A data point: after you made that change in the settings, - I had to close my browser (for my own reasons). When I opened the site again, I didn't experience the popup, and I was logged into the forum in the web browser.