if I understand correctly, you turn of the wireless interface, and the applet switch from the bar-meter to the green checked icon...
and you don't have a Ethernet cable plugged in ...
This is how it goes. As I am using my computer, at random times. The icon just switches to the check mark without me doing anything. While I am let's say here in the forum. I will look down and the check mark is there instead of the green bars. No cable plugged in. I use this computer only with wireless.
That was the behavior before the fix ... just to be 100% sure, check in synaptic about the package version, should be:
Then when I try to disconnect. It won't let me. Even if I shutdown and reboot it comes back. I have to quit it first. Shutdown and reboot, then it works right for a time then goes back to the check mark.
It's random so there is nothing to point at that I am doing. Now there could be something I do that I don't know about but there's the rub, I don't know about it.
I do appreciate all you are trying to do. Thanks
The next time it won't let you disconnect, try to left-click on the net_applet icon (will start network center), select the active interface, there is a button on the right bottom of the window, labeled "Disconnect/Connect", try to use that button, it could be a temporary workaround until a solution is found.
Additionally, whenever it should happen, try to run this command from a terminal:
dmesg | tail -15