'Update modified date' looks disabled in Ready to Publish

Description

Steps to reproduce:

1. Open a page and go to the Settings tab.
2. Select the 'Update modified date' check box.
3. Set the page to Ready to Publish. (Or to Ready for Review if a content approval sequence has been set on the page. In that case, approve the page so that it is set as Ready to Publish.)
4. Go to the page's Settings tab and look at the 'Update modified date' check box.

Expected result: The check box is selected.
Actual result: The check box is unselected.

Note: If you publish the page, the modified date is actually updated, even though the check box does not look selected.