I discovered a bug with villagers while playing on a superflat world.
As in the new 1.8 update villagers now harvest their crops and replant but I have discovered a bug where the villagers seem to replant only carrot crops in all types of farms. eg. in a 'wheat' or 'potato' sector of their farm they with harvest a fully grown crop but instead of replanting a wheat or potato seed they only replant a carrot therefore turning all farms slowly into carrot farms.