[racket] flat-rec-contract and vectorof

Hi all,

 > (define c
     (flat-rec-contract T
                        number?
                        (vectorof T)))
. . flat-rec-contract: expected flat contracts as arguments, got 
#<chaperone-vectorof>

I noticed there's a new section "Impersonators and Chaperones" in the 
doc. I'm not intending to deal with chaperone as I wrote the contract. 
Is this a bug, or is there a work around for my contract?

Chongkai