[NetSapiens]

I goofed around with this and couldn't get it to work as you described.

Then I started clicking the actual tabs in the preview window, as opposed to selecting the pages under the root page. Bingo! it resizes the preview window according to the size property.

So when I click the tabs, it firstly selects that particular page in the tree view, it also resizes the preview window.

EDIT: It is actually the size property of the page itself, NOT the root folder.. just read my own stuff, and thought that wasn't all too clear