The bug

Spiders and cave spiders jump and rotate randomly when there is a block 6 blocks above them, see the attached video Spiders jumping and rotating (17w06a).mp4.

Note: This might relate to MC-94054 but is not a duplicate because that bug happens without a block above them as well.

How to reproduce

1. Create a Superflat world with the following preset

   minecraft:stone,6*minecraft:air,minecraft:stone;127;
   

2. Go between the two stone layers and spawn spiders and cave spiders
   → After some time you should see spiders or cave spiders randomly jumping and rotating