Cannot create key for Azure AD application using Portal

Go to App registrations from AzureActiveDirectory. 

Created password credentials by patch manifest graph api: 

Now trying to create new key using azure portal:

Click Save, got error

F12 to see what wrong. Got 400 with message (Removed sensitve data)
{"ClassName":"Microsoft.Portal.Framework.Exceptions.ClientException","Message":"Graph call failed with httpCode=BadRequest, errorCode=Request_BadRequest, errorMessage=Update to existing credential with KeyId 'xyz' is not allowed., reason=Bad Request, correlationId = clientabc, response = {"odata.error":{"code":"Request_BadRequest","message":{"lang":"en","value":"Update to existing credential with KeyId 'abc' is not allowed."},"date":"2017-11-07T18:45:38","requestId":"requestID","values":[{"item":"PropertyName","value":"passwordCredentials"},{"item":"PropertyErrorCode","value":"KeyNotUpdatable"}]}}","Data":null,"InnerException":{"ClassName":"Microsoft.ActiveDirectory.PortalExtension.ADExtension.Server.AADGraph.AADGraphException","Message":"Graph call failed with httpCode=BadRequest, errorCode=Request_BadRequest, errorMessage=Update to existing credential with KeyId 'abc' is not allowed., reason=Bad Request, correlationId = clientabc, response = {"odata.error":{"code":"Request_BadRequest","message":{"lang":"en","value":"Update to existing credential with KeyId 'abc' is not allowed."},"date":"2017-11-07T18:45:38","requestId":"requestID","values":[{"item":"PropertyName","value":"passwordCredentials"},{"item":"PropertyErrorCode","value":"KeyNotUpdatable"}]}}","Data":{"graphError":{"code":"Request_BadRequest","message":{"lang":"en","value":"Update to existing credential with KeyId 'abc' is not allowed."},"values":[{"item":"PropertyName","value":"passwordCredentials"},{"item":"PropertyErrorCode","value":"KeyNotUpdatable"}]}},"InnerException":null,"HelpURL":null,"StackTraceString":" at Microsoft.ActiveDirectory.PortalExtension.ADExtension.Server.AADGraph.AADGraphMessageHandler.d__2.MoveNext() in E:\bt\861473\repo\src\ADExtension\Extension\Server\AADGraph\AADGraphMessageHandler.cs:line 69\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at