Only 1 page (and it's children, in this case) are by default selected with the "All pages" option

Steps to reproduce:

1. Login as Admin
2. Create at least a page
3. Edit another page eg. Sandbox Test Page 1
4. Create an AppWithinMinutes application
5. Add an entry
6. Go to Administer Wiki > Content > Export
7. Observe the default selections
8. Select "Created pages"
9. Observe the default selections
10. Choose 'All pages' from the drop-down on PAGES section
11. Observe the default selections
12. Click 'Export'
13. Save the XAR file
14. Create a subwiki
15. On subwiki, go to Administer Wiki > Content > Import
16. Upload and Import the XAR file

Expected results: All pages including unmodified extension pages are by default selected and exported.

Actual results: Only the first created page and it's children are selected and exported by default.

NOTE: After selecting "All pages" that makes only 1 page and it's children selected, it seems like the other selections get broken too.

If the user doesn't export the "All pages" and instead changes again the selection to "Created pages" or "Created and modified pages" the selection remains only to that page.