Spreaders only update their rotation visually when they face a mana pool or when right-clicked with a wand of the forest (or when applying/removing lenses):

• Facing mana pools (gif)
• Right clicking (gif)

Just to show what it did in 1.7:

• In 1.7 (gif)

The spreaders are still being rotated server-side, so the turntable does work.

Botania version: r1.8-0.6.4.2
Forge version: 11.15.1.1764