The text of the toggle link is "Switch to plain text editor" / "Switch to rich text editor". IMHO this is wrong.
You aren't switching to the "plain text" editor. You are disabling the "rich text" editor. (The configuration option is called "Show the disable/enable rich text editor toggle".)
This becomes very clear if you for some obscure reason have defined a CKEditor profile for plain text. Switching to plain text editor doesn't show the defined editor - only changing text format does.
I suggest using "Disable rich text editor" / "Enable rich text editor". Maybe the toggle doesn't have to use the work "rich" at all? You turn off the text editor and get a plain text area...
Just for the record: I think the behavior of the toggle is correct. I just think the text is wrong. The reason I care, is that translation these (misleading) texts to Norwegian makes the problem even worse ... Are we talking about a "plain/rich text" editor or a plain/rich "text editor"?
Sorry about the long text - feel free to shorten it.