You ONLY backcombed, correct? I only ask because I know that sometimes when other maintenance is used that it takes a while for the dreads to re-loosen and then grow out dreaded.
Have you made any changes to your routine, such as changing shampoo? Do you wear hats or ponytails often? What is your cleaning/drying maintenance like?
If you can give some explicit details on your hair over the past few months we may be able to narrow down the issue, if there is one.
ALSO: Re-backcombing will ALWAYS come out. Let your tips stay loose and they will eventually do their own thing. Re-backcombing the tips will only reset it back to day 0 or backcombing.