Yes, I agree this looks like a bug. I was seeing the same thing with the code generated route. Upon investigation it looks like the AppBar.IsOpen gets toggled to true during the right click, or swipe, but the CommandBar.IsOpen remains false. This fix worked for me:
BottomAppBar.Opened += (o, args) => { (this.BottomAppBar.Content as CommandBar).IsOpen = true; };