I've only got 19 viewstate items on this page when viewing it. When I edit the content with the 120+ versions, HtmlEdit.aspx has 7000+ viewstate items. There are 5 modules on the page and a search box. The 5 modules are HTML content (3), Site Statistics (1) and Google Translate (1). One of the html modules and the Google Translate are in ModuleWrappers. The module we're having the trouble with is not in a ModuleWrapper.
Removing the ModuleWrappers from the page doesn't stop the error from occuring.
Editing any of the other html content modules on the page does not produce an error.
It seems that the version paging is adding viewstate for all of the elements on all of the pages, not just the currently selected page.