Confluence 3 contains a permissions change whereby the "remove page" permissions is required to move a page.
The requirement for this change was to prevent users from moving pages from a space where they don't have "remove page" permission to a space where they do have "remove page" permission and then deleting the page. There is no reason for the "remove page" permission to be required in order to move a page within the same space.

The change was made to fix CONF-15047.