Alright, so I know that this has already been posted before, but that was over 3 years ago. I also know that this isn't seen as a bug, but a feature that is non-existent - but it really does feel like a bug!
All passive mobs in Minecraft are leash-able - except for the Villager (which is not counted as an "animal").
I find that annoying, since Villagers are the mobs that need them the most! They always run around and never go where I want them to go, and transporting them is awful...
You probably already know the issue, that the GUI pops up when you shift-right-click, and the villager isn't leashed. I would like to reach out one final time and ask the developers to make Villagers leash-able - maybe not in 1.10, but as soon as possible!
Kind regards, ~Henriko
The picture below portraits the marks of the current way players have to transport villagers.
if you know it's reported before, don't report it.
if you know it's said to be a feature request, don't report it.
right clickability of items not functioning on mobs with right click is already reported too.