Apparently closing the idle connections more aggressively is causing bad things to happen when messages are paused - I'm still unsure whether just in specific conditions, but I have been able to reproduce this fairly consistently in an http basic auth scenario. Here's how you can reproduce it:

In Epiphany go to https://wiki.collabora.co.uk/, wait for the basic auth dialog to show up. Wait for around 10 seconds and then type anything and hit ok. You will get this critical in the terminal, and the browser will not load the page nor ask for a password unless you hit enter in the address bar again:

libsoup-CRITICAL **: soup_session_get_connection: assertion `soup_connection_get_state (item->conn) != SOUP_CONNECTION_DISCONNECTED' failed

It seems when unpausing the message after providing the authentication information, the IO state indicates a read is being waited on. There is nothing new to read, though, so the connection is marked as idle.

+ Trace 227234

Then the session runs its queue and notices this connection idle and disconnects it, but does not detach it from the queue item. I was trying to write a fix for this, but I couldn't decide what is the expected behaviour here. Is the idle timeout being ignored? Should we try to keep the connection in an IN_USE somehow, should the message IO state be different, should we let the connection be killed and handle it by reconecting or none of the above?