Under Windows, it's possible to redock a floating pane by dragging it to the edge of the screen. This isn't possible under Ubuntu Linux 10.10.
Certain panes (in particular, the Slide Pane in Impress, and the Page Pane in Draw) don't contain a dropdown "View" menu in their header. X11 users therefore have no obvious way to redock these panes. Worse, undocking is a very simple action (click-and-drag), so users are likely to accidentally undock such panes and find themselves unable to redock them.
While it is possible to redock panes using Ctrl + double left-click, this isn't indicated anywhere except in a difficult-to-find part of the help documentation. Would recommend either that a Dock/Undock toggle button is added to the relevant panes' headers on X11 systems, or (if possible) drag-and-drop redocking is implemented on those systems as in Windows.
*** This bug has been marked as a duplicate of bug 42859 ***