Description of problem:

After performed project-wid search and replace in "search both mode", undo the replace will mistakely wipe out the uninvolved entries, which do not have the search term in target.

Version-Release number of selected component (if applicable):
Zanata version 1.7-SNAPSHOT (20120720-0026)

How reproducible:
Always

Steps to Reproduce:
1. Visit a document.
2. Find two rows  (row A and row B), that contains same word. Suppose the word is "TERM"
3. Click at row A, copy from source, but remove "TERM", save as approved
4. Click at row B, copy from source, save as approved
5. Click search and replace, and select "search both".
6. Search "TERM", click "select all",  and relace with "WORD"
   You should see that row B is replaced, but row A is untouched.
7. Click on notification panel, click "undo"
  
Actual results:
Content of row A is wiped out.

Expected results:
Content of row A is kept.

Additional info: