The bug

When shearing regular vines, they are unaffected by efficiency. Breaking a vine with unenchanted shears takes the same amount of time as breaking a vine with Efficiency V shears.

The expected behaviour is that the shears should break faster with the efficiency enchantment like the other blocks which shears are intended to be used on (e.g. wool)

To reproduce

1. Create any world in creative mode
2. Obtain two sets of shears
3. Enchant one to Efficiency V using an anvil or the /enchant command
4. Find a biome with natural vines or place vines on a wall
5. Switch to survival mode
6. Mine the vines with both sets of shears
7. The mining time will be identical