Redundancy is one of the five (I think five) fair reasons for dismissal. This means fair in the legal sense, rather than 'just'.
Are you still being paid the same deal on the redundancy terms as before - I sincerely hope so?
Assuming yes, the above, the deal is you are getting an extra three months contract, plus a bonus. If all that is true, then it makes sense to me that they are asking for a break in your service, because otherwise you could claim continuous service at the end of the extra three months, and having >1 year of continuous service opens the employer up to a potential claim.
Its rather a crude way to do it though.
Worth checking with ACAS as above.