Prop feather

Maybe I'm missing something but I cannot get the props to feather using either the mouse or the prop lever. I can shut down the engine with the mixture, back down the throttle to the stop but the prop still windmills. I can get it just a tad below the line in the VC showing Feather range but not below. And the prop will continue to windmill

However, if I also press SHIFT F2 on the keyboard, it will immediately feather the selected prop. I use FSUIPC to map all buttons and axis. Can't find anything in the documentation about a prop lock or stop - have I missed it?

Thanx,

Vic