Round Table for School Room #2: And why did my jointer do that anyway

My grizzly G0690X has been a very reliable maker of flat and straight boards.
So I was surprised that I ended up with bowed edges when I jointed these panels.
But I think I know what happened.
Somehow I’ve lucked upon good jointer technique in general, but I had to handle these panels differently. Normally when edge jointing I hook my left thumb over the top of the board, and that hand simultaneously presses the flat face of the board against the fence and applies downward pressure to hold the fresh edge down on the outfeed table. The right hand feeds the board.
But with 17 inch wide panels I can’t do that, so my left hand is pressing the panel against the fence but nothing is forcing it down on the outfeed. The weight of the panel is holding it down on the infeed. That doesn’t make a straight edge.

-- I intended to be a woodworker, but turned into a tool and lumber collector.