For some elements listed in Elements Explorer, the Used By context menu item is disabled. This prevents you from discovering which test the element is defined in. There's no error in the application log:

[08/21 14:36:12,Telerik.TestStudio.exe(15564:1)] First trace message from process 15564: "C:\Program Files (x86)\Telerik\Test Studio\Bin\Telerik.TestStudio.exe" 
[08/21 14:36:12,Telerik.TestStudio.exe(15564:1)] First trace message from foreground thread "Application start thread" (managed ID = 1, native ID = 16280).
[08/21 14:36:12,Telerik.TestStudio.exe(15564:1),Uncategorized] Orchestrator._iUIProject_ProjectClosed() : Project 'QACertification4000' Closed.
[08/21 14:36:18,Telerik.TestStudio.exe(15564:1),Uncategorized] Orchestrator.set_SelectedProject() : Active Project is : 'QACertification4000'
[08/21 14:36:18,Telerik.TestStudio.exe(15564:1),Uncategorized] Orchestrator._iUIProject_ProjectOpened() : Project 'QACertification4000' Ready.
[08/21 14:36:34,Telerik.TestStudio.exe(15564:8)] First trace message from pool unnamed thread (managed ID = 8, native ID = 19060).
[08/21 14:36:34,Telerik.TestStudio.exe(15564:8),TestStudio] <>c__DisplayClassf.<LoadInternal>b__9() : Extract elements time: 00:00:08.0004124
[08/21 14:36:34,Telerik.TestStudio.exe(15564:8),TestStudio] <>c__DisplayClassf.<LoadInternal>b__9() : Total Elements count: 5149
[08/21 14:36:35,Telerik.TestStudio.exe(15564:1),Uncategorized] Orchestrator._iUIProject_TestSelected() : Test 'WebTest' selected.
[08/21 14:36:38,Telerik.TestStudio.exe(15564:1),Framework] Manager.get_ActiveBrowser() : The current ActiveBrowser is either invisible or disconnected.
[08/21 14:36:38,Telerik.TestStudio.exe(15564:1),Framework] Manager.get_ActiveBrowser() : The current ActiveBrowser is either invisible or disconnected.
[08/21 14:36:38,Telerik.TestStudio.exe(15564:1),Framework] Manager.get_ActiveBrowser() : The current ActiveBrowser is either invisible or disconnected.
[08/21 14:36:38,Telerik.TestStudio.exe(15564:1),Framework] Manager.get_ActiveBrowser() : The current ActiveBrowser is either invisible or disconnected.

A sample project will be attached to the internal bug report.