mail() Bcc problem

OK, this used to work, but has recently stopped. In the mail() function, my fourth parameter used to be something like: "Bcc: bob@123.com". This scenario used to work perfectly, since I could potentially have a long list of people that I was mailing, and didn't want to show who all was getting the mail. However, in recent days this has stopped working. The mails still send perfectly if all of the addresses are in the "To" field, but then the mail list is exposed. Does anyone have any idea what might have caused this? I checked with the hosting company, and they said that neither PHP nor sendmail have been touched, so I guess it isn't that. :\ Please also mail back a response to bryan@razorhack.com. Thanks!!