Issue Summary

1. Page selection for custom exports broken when the total number of pages in the Space is high.

Steps to Reproduce

1. Create 11,000 pages, and split them under two parent pages, like so,

   • +--- Space Home
     |   +--- Parent 1
     |   |   +--- 5,500 sub pages
     |   +--- Parent 2
     |   |   +--- 5,500 sub pages
     

2. Go to Space Tools >> Content Tools >> Export >> Export PDF
3. Try a custom export, and selecting just Parent 1 and the pages under it, and just those pages would be exported.
4. Try a custom export, and select Parent 2, and the pages under it, and it will export only around 2000 or so of the pages.
5. If you were to add another sub page tree under Parent 2, and try exporting just the 500 pages with the parent page, instead of 501 pages, it will start exporting over 600 or so pages.
   • This number changes depending on the position of the sub page and the number of sub pages.

   • +--- Space Home
     |   +--- Parent 1
     |   |   +--- 5,500 sub pages
     |   +--- Parent 2
     |   |   +--- 5,500 sub pages
     |   |    |     + 500 sub pages.
     

6. An interesting thing to note is that if we were to move this 500 page and it's parent to the top of the Page tree, and selecting it, the number of pages being exported is correct.
   • So it seems the page selection is broken near the bottom of the list of pages.

Expected Results

1. The number of pages being exported should match the number of pages that is selected(ticked) in the custom export.

Actual Results

1. The number of pages being exported is different, sometimes more, and sometimes less than the number of pages that is selected.

Workaround

1. Currently, if we were to move the pages to the top of the Page tree, the export seems to work as expected.