From European boards: http://forums.wow-europe.com/thread.html?topicId=263836810&sid=1

The following changes to cleave have been made for the 2.1.0 patch.

–Cleaves will only hit people in front of the creature.
–Cleaves will have a chain length equal to the combat reach of the creature.

We still don’t have an exact estimate on when this patch will be ready but development is wrapping up and the test phase should begin relatively soon. As a reminder, the patch undergoes internal testing before public, PTR testing.

Note this does not seem to be something that will affect our cleave, but rather something that will make melee dps more viable in a lot of encounters. Currently the amount of 360 degree cleaves in the game make it tough to use rogues, enhance shamans, ret pallies and dps wars. This change will allow you to stay out of cleave as long as you are behind the mob, thus an indirect buff to arms (and fury) warriors!

Veritas