Unable to send to distros

[manypims]

My company is using a provider for Blackberry Enterprise Server service. All Blackberry devices on our network are unable to send e-mails to distribution lists. However, when the distribution list is "hidden", we can send to that particular distribution list. Our provider has escalated this to RIM and they are telling us it is a known issue between RIM and Microsoft and they are working on a solution. Has anyone heard of this problem and do you know of any solutions? Right now, we are creating a mailbox for key distribution lists and then forwarding that mailbox to the distribution list.