Okay problem solved...the reported symtoms were a little different than the actual, imagine that!
Anyway, it turns out that the users were not properly hanging up their phones and the call to voicemail was remaining active....and after a period of inactivity the CUE will default forward to the "voicemail operator", which in this case is configured as the console's primary number. Of course it appears to be one way voice when the console operator answers because she can hear what is going on in the calling parties office, but the calling party cannot hear her since their handset is sitting face down on the phone, but actually off-hook.
Morale of the story, pay attention to how the phones are hung up and watchout for those little handset tabs!