Can't break a link, all links are removed
 

I have a spreadsheet where I collect data from several others. Now I want do
exclude a few documents. How can I exclude 3 out of 10 without having to edit
the formulas? I tried Edit-Links and to break a link but the result is that
all links are removed. I can change from one document to another, but not
remove the link to a specific document. How can this be done?