When pressing ctrl-shift-m in edit mode, read-only mode is enabled.
In this mode, buttons like page-up, page-down, or going back to edit mode (ctrl-shift-m) do not work initially. They only work after the user has clicked in the document. It would be good to give the document focus automatically when entering read-only mode.
The same behaviour applies when entering read-only mode via the toolbar button or the entry in the 'edit' menu.
*** This bug has been marked as a duplicate of bug 89688 ***