I still can't reproduce it even with encryption set up, using an instant client, and logging in with a username that contains a dot.
I had an idea though - if you go to Options -> Editor -> Behavior, and check "Display SQL errors in popup dialog", then the first time you get the "connection is not connected" message - instead of it just going to the messages panel at the bottom, you'll get a popup with a "Reconnect" button.
Let me know if that works. Maybe "connection lost" type errors should always popup anyway, so you can reconnect w/o having to go to the main menu.
Also, please zip up and email me your user files folder, and I will try again with your settings. You can find steps to do that, along with my email address, here.