I used .NET snippet to add a data frame into ArcMap as bellow:
Dim pmap As IMap=mxDocument.maps.Create()
mxDocument.ActiveView = pmap
The newly created data frame 'New DataFrame' and it's features can be displayed in ArcMap, but it seems not a 'Normal' DataFrame. It can't be double clicked to show property, it doesn't shown in pagelayout and even can't be removed in ArcMap interface..
Maybe what code is missed?