how to use C-+ in isearch+? (was: Re: Copy/iSearch/Occur on folded outline view?)

[Gregor Zattler]

Hi Drew,
* Drew Adams <drew.adams@oracle.com> [05. Feb. 2013]:
> FYI, Isearch+ also provides toggle key `C-+' for this.
[...]
> http://www.emacswiki.org/cgi-bin/wiki/IsearchPlus

This is what I need to cope with my org files!

I installed and initialized it as described in the file.  

But when I do isearch-forward-regexp (which is bound to C-s in my
init.el) and then C-+ [1] cursor moves to the first `+' sign
which is in an invisible part of the file (actually a drawer in
an org file).

What am I doing wrong?

Ciao, Gregor

Footnotes:

[1] C-+ meaning Control-Key and the plus sign on the normal
keys, not at the keypad (which my laptop does not have), yes?

-- 
 -... --- .-. . -.. ..--.. ...-.-