Here I'm talking about lumps, bumps and loops. If you've had young dreads, then there's a pretty good chance you've had your fair share of lumps, bumps and loops. They occur when the lock shrinks up as it tightens, but often one part of the lock will shrink faster causing the slower and therefore looser part to get pushed out. Sometimes this creates just a lump, other time you'll get a loop of loose hair pushed out.
Over time the lumps and bumps will get flattened out a bit, but the loops will often stay indefinitely unless crocheted in or cut out. The majority of these characteristic effects will only occur on the original length as this is the bit that shrinks. The new growth will have far, far fewer mad bits.