ButtonGroup is marked as Unknown Component. (M300), but code runs fine

Hello, 

I ran in the bug as follows:

• I created a new Qt Quick Controls 2 Application.
• I added ButtonGroup { }
• EXPECTED: ButtonGroup to be accepted and qtcreator providing code completion etc.
• ACTUAL: it got marked red with in the tooltip saying: Unknown Component. (M300)
• The following works as a work around

  import QtQuick.Templates 2.0 as T; T.ButtonGroup { }

• Also Tools -> QML/JS -> Reset Code Model did not help.