You can play as much as you want to drag and drop the contents of tree controls exactly how you want them in the Control Panel. It doesn't work, nor has ever worked. Forum lists, too. These are actually sweet controls, but sorting isn't in their interactive UI lexicon.
To sort a File Gallery or other tree-based Community Server control use the Chameleon SortBy property on the web page. Here's an example:
<li class="DBVTTreeListItem">
<CSFile:GroupData ID="GroupData1" Property="Name" LinkTo="GroupHome" runat="server" />
<CSFile:FolderList ID="FolderList1" runat="server">
<QueryOverrides PageSize="999" SectionID="-1" SortBy="Name" />
<HeaderTemplate>
<ul class="DBVTTreeList">
</HeaderTemplate>