In snapshot 17w47b no icon appears in the Dock at all, for the launcher or the game.
Still persists in 17w47b
This does appear to happen only on macOS. This is standard behavior in macOS. Holding down shift disables scrolling due to the "Shift Scroll" feature.
Code may have to be implemented in Minecraft to get around this issue.
Aron Brown
In snapshot 17w47b no icon appears in the Dock at all, for the launcher or the game.