Changing citations

Dear list members, 

A patron encounters a very strange problem in Endnote X and Word 2003.
On my machine the same problem occurs with her files. I use Endnote
X.0.2.

When I edit a citation in the word document via Edit Citation(s), f.e.
add prefix "cf" 
then when pressing OK this citation and many others in the document are
replaced by other (irrelevant) citations. 

Any clue what might cause this problem and how it could be solved? The
patron uses the manuscript with endnote present at workplace and the
manuscript without Endnote present at home.

Best regards, 

Harrie Knippenberg 
Radboud University Nijmegen 
The Netherlands