(1) I believe that the patch I have fixes the bug I reported and the one Eli pointed out. And it does so without bringing a drastic change to the way the description string is generated.
(2) As for an extra binding that shows the complete list of all the active isearch modes, I agree with Drew that it can show a complete picture of what isearch is doing behind the scenes. @Drew: Can you please open it as a new bug report?