Weird waterfall

So I've let the FT-817 run Tx for a day. The last Rx I got was 0048Z with a local station (JH1HRJ) after that the band seemed dead. I get VK4TVL around 0900Z but on this day I was not able to hear him/her.

The attached file shows the waterfall I saw when I checked the laptop running WSPR-X. There is very pronounced "banding". On "normal" days everything will just be covered with noise (i.e. the bands aren't perceivable).

The radio has the optional Yaesu 2.3kHz option filter installed. Power is @ 1W. 13.8V from an Alinco switching PS.
WSPR-X is setup to have a TX of 25% only. Radio is well ventilated. Radio was warm to the touch but not uncomfortably warm.
There was a G2 geomagnetic storm yesterday (2015.05/19) but it probably have ebbed down by the time I got the screen capture.

Ideas anyone?

2015.05/22 I disabled the 2.3KHz filter on the radio. Still getting the banding.

Image icon 2015.05/19 6m banding137.32 KB
Image icon 2015.05/22 6m banding183.99 KB