Sorry, but I'm not sure I buy this BW chart.
Atttached Excel sheet with the measurements.
Well, I believe you made measurements and a chart - but that doesn't mean it's accurate.
Hell, you had HighRes mode on - which is an averaging technique, and thus a filter - which would normally be the last thing you should do if trying to accurately measure bandwidth.
But, IMO, if your measurements ARE correct, I'd say Rigol made a mistake in redesigning their filter - and it makes me feel better about owning a HW v.1