WPF Memory leak when trying to test modal dialogs.

When you try to open/close dialog window with testing framework it cause memory leak and child dialog not garbage collected. We do it in loop and for some iteration Telerik testing framework can't find dialog and break by timeout. 
We found it with windbg + sos dll. Results:

Scan Thread 14 OSTHread 25bc
DOMAIN(006A72D0):HANDLE(Pinned):1513e4:Root:  039593f8(System.Object[])->
  029ccf78(System.Collections.Generic.Dictionary`2[[System.IntPtr, mscorlib],[Telerik.TestingFramework.WpfExtension.WpfCommunication, Telerik.TestingFramework.WpfExtension]])->
  02a5650c(System.Collections.Generic.Dictionary`2+Entry[[System.IntPtr, mscorlib],[Telerik.TestingFramework.WpfExtension.WpfCommunication, Telerik.TestingFramework.WpfExtension]][])->
  02a4d990(Telerik.TestingFramework.WpfExtension.WpfCommunication)->
  02a4da38(Telerik.TestingFramework.XamlExtension.ClientProcessor)->
  02a4d9c4(Telerik.TestingFramework.XamlExtension.TechSpecific)->
  029cd424(MainApplication.ChildWindow)

It seems that some static dictionary is referenced to ChildWindow which cause memory leak.  It seems that problem in WpfCommunicationEntryPoint.Comms. I found only one static dictionary with this signature (problem can be in another place).

How to use windbg + sos.dll:
0. Run test from VS MemoryLeakSmokeTestFixture.MemoryLeak_TelericFramework
1. Run windbg 
2. File->Attach to process-> choose MainApplication
3. Load sos.dll : .loadby sos clr
4. Fild objects: !DumpHeap -type ChildWindow
5. Find who are referenced to it: !gcroot OneOfTheIntancesAdresses. 
 You are going to see the same results.

Sample project in attach

Thank you.
Looking for advice