ArgumentNullException can be thrown when opening a RadOpenFileDialog in the following scenario: CustomPlaces contains the Desktop directory, InitialDirectory is also set to Desktop and ShowNetworkLocations is false. 

System.Windows.Data Error: 8 : Cannot save value from target back to source. BindingExpression:Path=CurrentParentDirectory; DataItem='OpenFileDialogViewModel' (HashCode=57416810); target element is 'FileDialogsBreadcrumb' (Name='PART_PathNavigationPane'); target property is 'CurrentItem' (type 'Object') ArgumentNullException:'System.ArgumentNullException: Value cannot be null.
Parameter name: value
   at System.String.StartsWith(String value)
   at Telerik.Windows.Controls.FileDialogs.Helpers.PathHelper.CapitalizeNetworkPath(String path)
   at Telerik.Windows.Controls.FileDialogs.ExplorerControl.BringItemIntoView(DirectoryBaseWrapper itemToBring)
   at Telerik.Windows.Controls.FileDialogs.ExplorerControl.SyncTreeViewWithCurrentDir()
   at Telerik.Windows.Controls.FileDialogs.ExplorerControl.ProcessCurrentParentDirChanged()
   at System.ComponentModel.PropertyChangedEventHandler.Invoke(Object sender, PropertyChangedEventArgs e)
   at Telerik.Windows.Controls.ViewModelBase.OnPropertyChanged(String propertyName)
   at Telerik.Windows.Controls.FileDialogs.OpenFileDialogViewModel.OnPropertyChanged(String propertyName)
   at Telerik.Windows.Controls.FileDialogs.DialogViewModel.set_CurrentParentDirectory(DirectoryBaseWrapper value)'

Hi, we use the map control in our application.

We get random KeyNotFoundException in TilesDownloadManager when zooming in... 

System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
   in System.Collections.Concurrent.ConcurrentDictionary`2.get_Item(TKey key)
   in Telerik.Windows.Controls.Map.TilesDownloadManager.UpdateTileCache()
   in Telerik.Windows.Controls.Map.TilesDownloadManager.Process()
   in Telerik.Windows.Controls.Map.TilesDownloadManager.DownloaderThread()
   in System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   in System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   in System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   in System.Threading.ThreadHelper.ThreadStart()

System.Collections.Generic.KeyNotFoundException
  in System.Collections.Concurrent.ConcurrentDictionary`2[[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.__Canon, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]].get_Item(System.__Canon)
  in Telerik.Windows.Controls.Map.TilesDownloadManager.RemoveTile(Telerik.Windows.Controls.Map.TileId)
  in Telerik.Windows.Controls.Map.TilesDownloadManager.RemoveL1Cache()
  in System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
  in System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
  in System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
  in System.Threading.ThreadHelper.ThreadStart()

We use OpenStreetMapProvider and don't use tile caching.

The performance of loading the thumbnails is decreased with the removing of the cache in PdfViewer. 

Possible reason is that the pages are no longer loaded asynchronously.

Steps to reproduce:
- Open the SDK with the thumbnails for PDFViewer.
- Notice that the load of the thumbnails is slow.