[exim] problem with certain DNS lookups for NS records

let me cut it short:

set acl_c9 = ${lookup dnsdb{ns=152/29.160.221.217.in-addr.arpa}
{$value}{none}}

should give ns.ondecorte.net and instead it gives none. (I call it
from the DATA acl but this is irrelevant)

For the curious this is part of a semicomplex acl to find the NS
record of the smallest zone one IP belongs to.

Giuliano