I knew there was a thread somewhere. I hadn't realized quite how old it was...
I started building 9495 Gold Leader's Y-Wing yesterday and was surprised to find one of two red 1x2 jumper plates has a groove. The other is a "normal" non-groove jumper plate.
Much of my 1970s/1980s childhood LEGO had regular 1x2 and 2x2 plates without groove and I have often wondered why LEGO then added the groove to regular plates but not to jumper plates. Seems they have "fixed" that now.
According to BrickLink part 3794b
has been around since 2009 as an alternate, but this is the first one I've ever come across.
I myself actually prefer all plates non-groove because then you can't see the join with the brick below, but what always bothered me most was the messy look along the edge when mixing groovy regular plates and non-groove jumper plates.