This was working before upgrading to the recently released Q2 service pack.
I'm adding nodes with subnodes and defaulting them all to checked. The treeview is inside of a PageView and the multipage has the following settings:
"border: 1px solid gray"
When I click the tab to go the second pageview, the treeview checkednodes collection is empty. The treeview nodes then become unchecked. However, if I change the RenderSelectedPageOnly to false, they will remain checked and everything works as expected. I believe something was broken in the latest release.