I think that you're rigtht it's a new part, but I believe it could also be a 1x3 round slope, with a 'plate 1x1 sized'-cutout at the bottom of one end. There seems to be a real gap there, to me it doesn't look like it's filled up with a clear 1x1 plate.
Dit someone already mention that, when you look at the available parts, the two models of the top picture seems to be alternatives of the #7239 set? Or am I now saying something that was already obvious to everyone here?
With friendly greetings, M. Moolhuysen.
I cannot say it was obvious to me but now that you said it... Yes, you seem to be right :-D