Problem referencing a cell with formula in same position of other file

Step to Reproduce

1. visit demo http://zssdemo.zkoss.org/zssdemo/reference_to_another_workbook
2. clear all content of 2 books
3. enter 1, 2 at A1, 2 at B1 in profile.xlsx
4. at C1 in profile.xlsx, enter =SUM(A1:B1) (must enter a formula)
5. enter =[profile.xlsx]Source!C1 at C1 in resume.xlsx
6. delete content at C1 in resume.xlsx
7. paste the same formula above, =[profile.xlsx]Source!C1, at the same cell, C1

Actual Result

value of C1 cell in resume.xlsx is #N/A