When aggro on a player, cave spiders are able to attack through up to one block of solid obstruction. This did not happen before 1.8.0.

Please see video at this link for demonstration: https://www.youtube.com/watch?v=29fvWUg1_oY

In the video, the bug is demonstrated on a Vanilla Survival server. The XP farm it is demonstrated at was designed in a creative superflat world with a different seed, at the same coordinates as the server. In case this is a positional bug, a 1.7.10 and 1.8.0 version of the creative world are linked below for testing purposes.

1.7.10 files: https://www.mediafire.com/?h7brq1o33vgyy9y
1.8.0 files: https://www.mediafire.com/?h7brq1o33vgyy9y