The pagination node disappears from the wiki export tree after clicking once on "xx more..."

Follow this steps to reproduce:

• Configure your user profile to show hidden pages (in order to see many pages in the tree)
• Go to Wiki Administration > Content > Export
• The tree loaded for the "Created and modified" pages shouldn't have a pagination node (that's a precondition for the issue)
• Switch to the "All pages" filter
• Click on the "xx more.." node, provided xx > 15 (so that a new pagination node is required afterwards)
• The pagination node for the remaining xx - 15 nodes is missing from the tree, so you can't see those nodes