Word does not update NUMPAGES when multiple master pages are used

[Kumaraswamy]

I have a document with 2 pages. I've set fields {PAGES} and {NUMPAGES} in the footer section and then unlink the same as previous in the second page footer section.
This results in "1 / 1" in footer section in page 1 instead of "1 / 2"

Exact steps to replicate the issue.

1. Create new document
2. Insert section break (next page)
3. Edit first page footer
4. Insert fields: { PAGE } { NUMPAGES }
5. Unlink second page footer from previous.
6. Save document

I've seen this issue in Word 2010 and 2013.