For the time being the following workaround can be used:
		<telerik:RadFileExplorer ID="RadFileExplorer1" runat="server" Width="230px" Height="430px" DisplayUpFolderItem="true"
			ExplorerMode="FileTree">
		</telerik:RadFileExplorer>
		<script>
			Telerik.Web.UI.RadFileExplorer.prototype._onTreeContextMenuItemClicked = function (sender, args) {
				var treeNode = args.get_node();
				var menuItem = args.get_menuItem().get_value();
				switch (menuItem) {
					case "Rename":
						treeNode.startEdit();
						var nodeInput = treeNode.get_inputElement();
						if (!this._allowFileExtensionRename) {
							var item = this._createItemFromTreeViewNode(treeNode);
							if (!item.isDirectory())
								nodeInput.value = $T.FileExplorerHelper.stripExtension(item);
						}
						this._attachFileNameValidator(nodeInput);
						var treeUL = sender.get_childListElement();
						this._treeKeyDownDelegate = Function.createDelegate(this, this._treeKeyDown);
						if (treeUL) $telerik.addHandler(treeUL, "keydown", this._treeKeyDownDelegate, true);
						break;
					case "NewFolder":
						if (!this._isNodeADirectory(treeNode)) {
							treeNode = treeNode.get_parent();
						}
						var nodeValue = treeNode.get_value();
						this.createNewDirectory(nodeValue);
						break;
					case "Delete":
						var selItems = sender.get_selectedNodes();
						var delItem = new Array();
						for (var i = 0; i < selItems.length; i++) {
							var currItem = this._createItemFromTreeViewNode(selItems[i]);
							delItem.push(currItem);
						}
						this.deleteItem(delItem);
						break;
					case "Upload":
						this._showUploadWindow();
						break;
					case "Copy":
						var selectedItem = null;
						if (!treeNode.get_selected()) {
							selectedItem = this._createItemFromTreeViewNode(treeNode);
						}
						this._copy("tree", selectedItem);
						break;
					case "Paste":
						var pasteItem = this._createItemFromTreeViewNode(treeNode);
						this._paste(pasteItem);
						break;
				}
			}
		</script>

TreeView context menu remains visible when a permission alert is shown. I should be hidden like the Grid contect menu is.

Video:

https://screencast-o-matic.com/watch/crlYQMV2dzP

Steps to reproduce:

1. Copy a file from the Grid in RadFileExplorer

2. Right click over the same directory in the TreeView and select Paste

Result:

have found similar issue :  http://www.telerik.com/support/pits.aspx#/details/Issue=5296
which look like has been fixed, but unfortunately for following case it doesn't:
We still have performance issue, in following situations:
   - when content root folder contains few (1-5) subfolders
   - one of subfolder contains lot of (200-500) sub-subfolders 

then first time RadFileExplorer  loading to long (aproximatelly 3-5min). after some researching has been found that problem in the method:  

     private bool HasSubFolders(string virtualPath);

which instead of simply check that folder isn't empty (exist any one file or directory)  always construct complete version of the subtree (in the example above - subtree contains 200-500 subfolders, each of them checking for content, permission etc - that is why it takes time). Probable to check that node  HasSubFolders, RadFileExplorer  could execute new virtual method of the FileSystemContentProvider bool HasSubFolders. In that case: FileSystemContentProvider (or inherited classes) will decide that Folder contains SubFolders.

Steps to reproduce:

http://demos.telerik.com/aspnet-ajax/fileexplorer/examples/overview/defaultcs.aspx

       1.  Delete Flower3.jpg
       2.  Rename Flower5 to Flower3

Actual: The image with Flower3 name has changed to the one which was deleted

Cross folder searching/filtering please.

It is not possible to select a Toolbar item in RadFileExplorer on Enter press if the control is used in Lightweight render mode.

Steps to reproduce:

1. Open https://demos.telerik.com/aspnet-ajax/fileexplorer/examples/keyboardsupport/defaultcs.aspx

2. Press "Ctrl+f2" to focus RadFileExplorer

3. Press "Shift+1" to focus its toolbar

4. Use the Arrow keys to navigate between to Toolbar items

5. Press Enter over a button (e.g. Upload)

Result: The command is not triggered

Workaround: The issue is not reproducible in Classic render mode.

It is not possible to navigate between ContextMenu items with the arrow keys when the Keyboard support is enabled.

The ThreeView remains the focused element even after the ContextMenu is shown and using the arrow keys navigates through the tree nodes instead of the ContextMenu items.

Steps to reproduce.

1. Click somewhere on the page and press "F" for focus FileExplorer
   
2. Press "T" to focus TreeView
3. Press "C" to show tree context menu
4. Pres Up/down arrow to navigate through the context menu items

Result: The navigation occurs in the three instead of the Context menu

            <telerik:RadFileExplorer ID="RadFileExplorer1" Height="380px" Width="750px"
                AllowPaging="false" EnableCopy="true" runat="server">
                <Configuration EnableAsyncUpload="true" SearchPatterns="*.*" UploadPaths="~/Images/" DeletePaths="~/Images/" ViewPaths="~/Images/"></Configuration>
            <KeyboardShortcuts
                FocusFileExplorer="F"
                FocusAddressBar="A"
                FocusToolBar="B"
                FocusTreeView="T"
                ContextMenu="C"  
                />

FileExplorer does not scroll its tree properly to the programatically selected folders.

Steps to reproduce:

1. Set a nested folder with a long path programatically:

fileExplorer.set_currentDirectory("/images/AAA/FolderA1/FolderA2/FolderA3/FolderA4/FolderA5")

2. Select another nested folder programatically:

fileExplorer.set_currentDirectory("/images/BBB/FolderB1/FolderB2/FolderB3/FolderB4/FolderB5")

Result: The second folder is selected, but the TreeView does not properly scroll into view containing it.

A JavaScriptError is thrown when FileExplorer with enabled AsyncUplaod is used for multiple files uploading in IE. The message of the error is:
JavaScript runtime error: Object doesn't support property or method 'get_allowMultiRowSelection'

Steps to reproduce:
1. Open http://demos.telerik.com/aspnet-ajax/fileexplorer/examples/asyncupload/defaultcs.aspx in IE10
2. Open the FileExplorer's Upload dialog
3. Select 2 or more files for upload
4. Click the Upload button

Result: A JavaScript error is thrown.

RadFileExplorer only natively works with standard Windows files that are on the server.  This precludes us from effectively using Azure's data structures, especially blob and the newer file types. With things like Webjobs where there is no standard file structure, we need the ability to access files that are stored in a shared space.

When users quickly select different folders in the TreeView and content is still loading, the caching mechanism of FileExplorer fails and loads incorrect data to the last selected folder. 

FileExplorer built-in features I would like to see:
1. Support for UNC paths so that the root folder may be located in a network share as opposed to a folder under the application folder.
2. Support for sub-pathing so that it can be dynamically programmed to support direct display of target folder without having to navigate to the target folder
3. Built-in Delete function to complement the built-in Upload function
4. Optional display of checkbox column to allow for multiple selection for items to be Deleted or Downloaded
5. Built-in Progress Bar for Upload and Download functions

Please consider adding file editing into the RadFileExplorer (could leverage CodeMirror).  Would be a great help to sitefinity to be able to edit the css or less directly on the fly in the fileexplorer.

Such property will allow the developer to choose whether the warnings will be displayed as RadAlerts or standard browser alerts. In this way the built in WindowManager could be user for showing RadAlerts.

Add configurable option to create a thumbnail for uploaded image and use it in the thumbnail preview mode if one is available