This is normal.
When you open the DevTools window, ChromeDriver is automatically disconnected. When ChromeDriver receives a command, if disconnected, it will attempt to close the DevTools window and reconnect.
Chrome's DevTools only allows one debugger per page. As of 2.x, ChromeDriver is now a DevTools debugging client. Previous versions of ChromeDriver used a different automation API that is no longer supported in Chrome 29.
If you need to inspect something in DevTools, the best you can do now is pause your test so that ChromeDriver won't close DevTools. When you are done inspecting things in Chrome, you can unpause your test and ChromeDriver will close the window and continue.
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