Just the opposite - if your PTR record doesn't contain in-addr.arpa it probably won't work, unless there's some CNAME jiggery-pokery goin' on. :)Marginally more seriously if your reverse DNS has in-addr.arpa in the final result (as opposed to the left hand side of the record, or any intermediate CNAMEs or glue records) then, yeah, you've probably made a mistake.
Comments policy: Al is always right. Kidding, mostly. Be polite, and you're welcome to join in, even if it's a differing viewpoint.